Forbes also has its own rich list with slightly different numbers.

Mr Bezos is at the top of that list ($US186.9b), with Mr Musk a distant second ($US166.1b).

The Tesla CEO's comments about the "high" price of bitcoin came two weeks after his electric car company said it had invested $US1.5 billion in the volatile digital currency, and would accept it as a payment method in the "near future".

Bitcoin hit a record high of $US58,354 on Monday, having surged more than 400 per cent in the past year.

But overnight, the cryptocurrency suffered its biggest daily drop in a month, falling to as low as $US45,000 on scepticism about its "sky high" valuations.

Mr Musk's net worth is heavily tied to his electric vehicle company's share price.

Tesla shares plummeted by as much as 13 per cent overnight, but trimmed their losses to just 2.2 per cent by the time Wall Street finished trading.

This was on top of Tesla's 9 per cent slump yesterday.

Bitcoin is both a "friend and foe" for the Tesla boss, Wedbush Securities analyst Daniel Ives said.

"While Tesla on paper made roughly $US1 billion on bitcoin in a month that exceeded all its EV [electric vehicle] profits from 2020, the recent 48 hour sell off in bitcoin and added volatility has driven some investors to the exits on this name in the near-term," he said.

"We continue to believe the bitcoin move was a strategic one for the long-term and will have a ripple impact as Square, Mastercard, Microstrategy and now Tesla embrace bitcoin."

Overnight, the payment platform company Square said it bought an extra $US170 million worth of bitcoin. That was on top of its $US150 million purchase in October last year.

ASX falls, as Aussie dollar briefly hits three-year high

The local share market's losses accelerated on Wednesday afternoon, after a volatile night on Wall Street.

By 4:20pm AEDT, the benchmark ASX 200 index closed 61 points lower (-0.9pc) at 6,778 — back to where it was a couple of days ago. 

The broader All Ordinaries index had fallen by a similar level, to 7,049 points.

Some of the best performers were Nine Entertainment (+9.7pc), Blackmores (+6.3pc), Bega Cheese (+6.2pc), Viva Energy (+6pc) and Worley (+4.5pc).

Shares in the mining giants suffered heavy falls, including BHP (-3.1pc), Rio Tinto (-2.7pc) and Fortescue Metals (-1.4pc).

In banking, NAB was the only member of the big four to rise (+0.4pc), while Commonwealth Bank, Westpac and ANZ fell between 0.4 and 0.7 per cent each.

Meanwhile, the steepest falls were felt by infection prevention company Nanosonics (-8.1pc), Seek (-7.8pc), Downer EDI (-6pc), AGL Energy (-4.5pc) and REA Group (-4.4pc).

Nanosonics' shares tanked after the company reported that its first-half profit fell (-74pc) to $1.46 million.

Shortly after midday, the Australian dollar jumped to a three-year high of 79.44 US cents.

But the local currency has given back those gains, and last traded at 79.1 US cents.

It received a short-lived boost after the Bureau of Statistics (ABS) revealed that Australian pay packets went up (+0.6pc) in the December quarter, which was a better-than-expected result.

However, wage growth over the year remained at a record low of 1.4 per cent.

The price of Australia's key export, iron ore, fell (-1.7pc) to $US173.05 a tonne.

Nine, SeaLink, WiseTech and Appen earnings

Nine Entertainment shares jumped (+9.7pc), after the network reported a half-year profit of $181.8 million, helped by advertisers spending more as Australia better controlled the coronavirus.

Shareholders will receive an interim dividend of 5 cents per share, fully franked. This was the same as the previous interim payout.

Shares in logistics software company WiseTech Global lifted (+1pc) after the company reported its first-half profit fell (-26pc) to $44.4 million.

However, WiseTech's revenue rose (+16pc) to $238.7 million. The company also expects its full-year EBITDA (earnings before interest, tax, depreciation and amortisation) to be between $165 million and $190 million (or growth of 30 to 50 per cent).

WiseTech will pay an interim dividend of 2.7 cents per share.

Meanwhile, the artificial intelligence company Appen saw its share price slump (-12.1pc) after reporting its annual profit rose (+21.4pc) to $50.5 million.

It declared a final dividend of 5.5 cents per share (10 per cent higher than last year's payout).

But Appen forecast that its full-year underlying EBITDA would be in the range of $120 million to $130 million, which was lower than the market had expected.

SeaLink Travel Group was one of the biggest movers on the market. Its share price surged 13.7 per cent to $8.03.

The company provides transport, including bus and light rail services, in Australia, London and Singapore.

Its purchase last year of Transit Systems Group helped first-half net profit jump to $32 million (up from $8.7 million in the prior corresponding period).

Pandemic boosts Woolies profit

Supermarket giant Woolworths posted a 28 per cent jump in first-half net profits to $1.135 billion (on a 10.6 per cent rise in sales to nearly $36 billion).

Chief executive Brad Banducci said strong growth in food, BIG W and liquor offset a hit to earnings from COVID restrictions in the group's hotels, and a rise in costs.

"The first half of financial year 2021 continued to be impacted by COVID, with elevated sales and higher costs as we worked to maintain a COVID-safe environment for our customers and team," he said.

Mr Banducci pointed to previously struggling discount department store BIG W as a "particular highlight", with its earnings up 166 per cent on the prior year.

Woolworths said eCommerce sales increased by 92 per cent to $1.8 billion in the half.

The company will pay a dividend of 53 cents per share, up 15.2 per cent on last year's interim payout.

The result was moderately pleasing to the market, with Woolies shares up (+1.1pc) to $39.50.

COVID-19 slams Scentre profits

On the other end of the retail spectrum, shopping centre operator Scentre Group, which runs Australian Westfield malls, reported a $3.73 billion full-year net loss for 2020.

The massive loss was driven by a $4.25 billion write-down of its property valuations over the past year, as foot traffic dried up due to the pandemic and shoppers shifted more of their spending online.

However, Westfield said demand for space remained strong, with 98.5 per cent of its portfolio leased as at December 31, 2020.

Despite the accounting losses, Scentre is paying a 7-cent dividend out of its $763 million annual operating profit.

Scentre shares fell (-1pc) to $2.84.

Sydney Airport appoints Gonski as chairman

Another company hit hard by the pandemic — arguably one of the hardest — is Sydney Airport.

It reported a full-year net loss of $107.5 million, with passenger traffic down by around three-quarters on the previous year.

The result would have been even worse were it not for the first couple of months in 2020 where international and domestic travel was operating as normal – over the last three quarters of 2020 the airport's passenger traffic was down 93.4 per cent.

"The COVID-19 pandemic has delivered a crisis of unprecedented magnitude to the global aviation industry, and Sydney Airport has been right on the frontline, both operationally and financially," chief executive Geoff Culbert said.

The airport raised $2 billion from shareholders last year and will not pay a dividend, and has also secured nearly $1.5 billion in debt funding and facilities.

Sydney Airport has also appointed David Gonski as its next chairman. He will succeed Trevor Greber, who will step down at the company's annual general meeting on May 21.

Mr Gonski was formerly the chairman of ANZ, Coca-Cola Amatil and sat on the boards of many other companies.

He was also the chairman of the former Gillard government's review into school funding (the Gonski Report), which was scrapped by the subsequent Abbott government in 2013.

Sydney Airport's share price jumped (+2.5pc) to $6.08.

Medibank profits during pandemic

Private health insurer Medibank has profited during the pandemic, citing it as a key reason why an increasing number of Australians took out policies last year.

Medibank said it had a 49,000-strong net increase in resident policyholders, underpinning a 27 per cent increase in net profit to $226 million.

"While it is far too early to say the decline in industry participation has definitively bottomed, the private health insurance market has proved increasingly resilient," Medibank chief executive Craig Drummond said.

Mr Drummond highlighted growth in its premium Medibank brand, which picked up an extra 17,600 members over the half-year.

The company will pay an interim dividend of 5.8 cents per share.

Mr Drummond also announced he plans to leave Medibank, and the company has begun a search for his replacement.

Medibank's share price fell (-3.5pc) to $2.79.

Recent bitcoin rally not 'sustainable'

The volatile digital currency bitcoin plummeted as much as 17 per cent overnight as investors grew nervous at sky-high valuations, sparking a sell-off across cryptocurrency markets.

After dropping to as low as $US45,000, it managed to recover some of those losses.

Bitcoin is still down at $US46,492 on Wednesday morning, a 15.2 per cent slump in the past 24 hours.

"The kinds of rallies we've been seeing aren't sustainable and just invite pullbacks like this," senior market analyst at OANDA, Craig Erlam, said.

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"It was an extremely overbought market."

The drop took its losses to over a fifth from a record high of $US58,354 hit on Monday, and underscored the volatility of the emerging asset. However, it was still up around 60 per cent since the start of the year.

Ether, the world's second largest cryptocurrency by market value, dropped (-143pc) to $US1,545.

Its price often moves in tandem with bitcoin, and has shed more than 30 per cent of its value since last week's record peak.

Crypto markets have been running hot this year as big money managers and companies begin to take the emerging asset class seriously, piling money into the sector and driving confidence among small-time speculators.

The cryptocurrency's rapid gains in recent months have led to calls from governments and financial regulators for tighter regulation.

US Treasury Secretary Janet Yellen said earlier this week that bitcoin was extremely inefficient at conducting transactions and was a highly speculative asset.

Bitcoin's high volatility, critics say, is among reasons that it has so far failed to gain widespread traction as a means of payment - an expectation that has in part fuelled its rally.

Square puts more 'skin in the game' with bitcoin

The mobile payments firm Square has bought an extra $US170 million worth of bitcoin, and its chief executive Jack Dorsey has promised to "double down" on its commitment to the world's biggest cryptocurrency.

"The Internet needs a native currency, and we believe bitcoin is it," said Mr Dorsey, the longtime bitcoin enthusiast who is also the CEO of Twitter.

Square bought 3,318 bitcoins in the December quarter, adding to the mainstream acceptance of the digital currency that has been winning support from several big investors.

"By us owning bitcoin, our incentives are aligned with skin in the game," Dorsey said on a post-earnings conference call with analysts.

Square has been involved with the currency for years and its Cash App, a payments service, has allowed users to trade it since 2018.

The app had three million active bitcoin customers in 2020, with a million new users buying the cryptocurrency for the first time in January, the company said.

In October last year, Square bought about 4,709 bitcoins at around $US50 million.

In its latest purchase, Square paid more than $US51,200 per bitcoin, according to Reuters' calculations, which is far higher than they were currently worth.

Square's revenue in the quarter more than doubled to $US3.16 billion, which the company said was helped by bitcoin purchases on Cash App.

Square's gross profit on bitcoin trading rose 13 times in the December quarter, but it was still just a minor part (2pc) of its revenue from the cryptocurrency.

Its bitcoin holdings are now worth about 5 per cent of its $US4.4 billion cash pile.

The company posted adjusted earnings of 32 US cents per share, beating market expectation of 24 US cents.

Its share price on the New York Stock Exchange fell (-4.3pc) to $US256.59 per share.

Tech sell-off continues

US markets experienced another volatile day, with the Dow, S&P and Nasdaq all in negative territory, earlier on Tuesday local time.

However, market sentiment recovered sharply in the final hour of trade.

The Nasdaq Composite closed (-0.5pc) lower at 13,485 points. At its worst, the tech-heavy index had plunged 4 per cent before its eleventh-hour turnaround.

The Dow Jones index went up 14 points (flat) to 31,631 (after recovering from a 360-point drop overnight).

The benchmark S&P 500 reversed a 1.8 per cent loss, ending marginally higher (+0.1pc) to 3,890 points.

Apple's share price was slightly weaker (-0.1pc), after falling 6 per cent earlier in its up-and-down session.

The S&P energy sector was the best performer, gaining 1.6 per cent thanks to soaring oil prices.

America's oil and gas stocks have jumped almost 27 per cent since the year began.

"People are buying the dip, a move that's been rewarded for months in a one-sided market," said Dennis Dick, head of market structure and a proprietary trader at Bright Trading.

The decline in tech stocks and rise in value stocks, along with copper and crude oil, show investors are rotating into assets that are expected to do well in an improving economy, Fawad Razaqzada, market analyst at ThinkMarkets in London, said.

But the equity decline is a warning sign that risks must be heeded and investors should not be so reckless or deceived by markets at extremely high levels, he added.

"It's more of a rotation story than of stocks topping out. So the dips will be bought," Mr Razaqzada said.

"The market is up almost in a straight line. You've got to have the market correct."

Oil prices jumped overnight, underpinned by optimism over COVID-19 vaccine rollouts and lower output as US supplies were slow to return after a deep freeze in Texas shut crude production last week.

Brent crude futures lifted (+0.9pc) to $US65.84 per barrel.

Gold slid as the dollar rebounded from six-week lows, with spot prices falling (-0.2pc) to $US1,805.05 an ounce.

Fed won't turn off stimulus taps, Powell reassures market

Wall Street's late-stage recovery was helped by Federal Reserve chair Jerome Powell, who gave some reassuring remarks when he testified before the US Senate Banking Committee overnight.

Mr Powell said the US economic recovery remained "uneven and far from complete", and that it would be "some time" before the Fed considered changing policies aimed at helping regain full employment.

He also pushed back on suggestions the Fed's zero interest rate and quantitative easing policies — colloquially referred to as "money printing" — risked unleashing inflation and financial risks in what may be an emerging economic boom.

"Monetary policy is accommodative and it continues to need to be accommodative," Mr Powell said.

"Expect us to move carefully, patiently, and with a lot of advance warning," before any changes, he added.

This was in response to questions from Republican lawmakers about whether a faster-than-expected recovery still required crisis-level stimulus measures.

When asked what his message was to financial markets, Powell did not talk about the risks of rising bond yields or a possible spike in inflation, but of the roughly 10 million jobs still missing compared to a year ago, and the need for the US central bank's policy to stay wide open until that is fixed.

Interest rates will remain low and the Fed's $US120 billion in monthly bond purchases will continue "at least at the current pace until we make substantial further progress towards our goals ... which we have not really been making," Mr Powell said in the hearing.

In summary, the Fed chair believes monetary policy needs to be supportive and that there is a long way to go to repair the jobs market and before inflation becomes a concern, Michael Arone, chief investment strategist at State Street Global Advisors in Boston, says.

"I'm not anticipating any changes to monetary policy any time soon," Mr Arone said, a view that should ease market concerns that the Fed could boost interest rates to tap down inflation.

ABC/Reuters/AAP