Donald Trump says he will cut the corporate tax rate from 21 per cent to 15 per cent "solely for companies that make their product in America", while Kamala Harris wants to increase the corporate rate to 28 per cent, describing it as "a fiscally responsible way to put money back in the pockets of working people and ensure billionaires and big corporations pay their fair share".

In a speech to the Economic Club of New York, Trump said he would protect American industries if he is reelected by increasing tariffs on imports while cutting other taxes and regulations.

The former US President's proposal would deepen his 2017 tax cut, which reduced the corporate tax rate from 35 per cent.

"I am promising low taxes, low regulations, low energy costs, low interest rates, secure borders, low, low, low crime," the Republican said before an audience of key business leaders.

"We want to make our goods in America — and most of them we can.

"If you outsource, offshore or replace American workers, you are not eligible for any of these benefits."

While a 15 per cent corporate rate would represent a major win for large US corporations, analysis, based on the University of Pennsylvania's Wharton Budget Model, suggests it would add between $US4.1 trillion and $US5.8 trillion to America's national deficit over the next decade.

It would also mean big companies end up paying far lower rates than smaller, privately held businesses, where rates can be as high as 37 per cent.

Trump also vowed to establish a taskforce to review federal expenditures — an idea recommended by Tesla and SpaceX chief executive Elon Musk, who has thrown his support behind Trump.

"Elon — because he's not very busy — has agreed to head that task force," Trump joked about tapping the world's richest person.

Trump said the commission would be "tasked with conducting a complete financial and performance audit of the entire federal government and making recommendations for drastic reforms".

Trump's proposal is in direct opposition to Democratic presidential candidate Kamala Harris's plan for corporate taxes.

Goldman Sachs analysts estimate the proposed Harris corporate tax hike could reduce S&P 500 company earnings by about 5 per cent, with additional taxes potentially hitting profits harder.

Ms Harris also has called for a 28 per cent capital gains tax on people that earn $US1 million or more. Millionaires would have to pay a minimum tax on their unrealised capital gains from assets such as stocks, bonds, or privately held companies.