Allan Qi did not plan on becoming a property investor.

The 32-year-old bought an apartment in Sydney's western suburbs six years ago to live in, but when he moved to Melbourne, he became a landlord.

But he is also a tenant and has lived in the same house in Melbourne's eastern suburbs for the past five years.

The apartment is negatively geared, so the rent he receives does not cover the mortgage repayments.

It's a struggle to balance the budget

With a household income of about $90,000 a year, technology and design teacher Allan and his wife Juan are already struggling to keep up with their expenses.

They are concerned about how high interest rates might go.

"Very, very nervous, very anxious about what's the go for the future," said Mr Qi.

Their investment loan is currently fixed but when that ends, Allan says they will have to raise the rent or sell.

At the same time, he does not know what his landlord will do.

"I've been trying to avoid [putting the rent up] just because being a tenant myself, I understand that we're all struggling a bit," said Mr Qi.

"But because that interest rate will rise quite a bit, I'm going to have to pass it on to be able to continue surviving."

The rental market is already in crisis

That is exactly what many of Australia's 2.8 million renters are concerned will happen, says acting chief executive at the Australian Council of Social Services (ACOSS), Edwina MacDonald.

"People are really fearful of what the interest rates rising will mean for renters, that landlords will be passing the increasing rates on to renters."

After years of record-low interest rates, the Reserve Bank started lifting the official cash rate in May to combat rising inflation.

Fixed rates are already going up.

And there will be many more rate rises to come, with RBA governor Philip Lowe indicating the cash rate could reach 2.5 per cent (or beyond, as some economists are predicting).

That means many of the variable rates that lenders charge borrowers could hit about 5 per cent or more.

It is difficult to determine exactly how much rate rises have influenced rental increases so far, particularly as rents might be increased at different stages during the year. But prices continue to rise.

"Since the first interest rate rise on our rentals index, rents have gone up by another 2.4 per cent nationwide," said Louis Christopher from SQM Research.

The rental market has been tight for months. National vacancy rates sit at just 1 per cent, the lowest in 16 years.

"It's a really tough market at the moment," said Joel Dignam from Better Renting.

"The size of the rents [increases] that we're seeing and the inflexibility from landlords is quite concerning."

Rental prices are rising across the country

The lowest vacancy rates are in regional coastal areas, including the Gold Coast, northern New South Wales and the Mornington Peninsula in Victoria.

People moved to these locations during the pandemic, but there just are not enough houses.

Lack of supply has pushed prices up around the country — the nationwide median rent is sitting at $510 a week.

In Canberra, Dom Cradick is packing up his house in the inner north.

He and three housemates have lived there for the past six years but in May, they received an email from their agent saying the rent would be going up $50 a week to $900 — the biggest rent increase they had ever had.

"We said we wouldn't pay more than $20 [extra] a week, that's how much our wages have grown in that amount of time," Mr Cradick said.

"Now we're moving out."

But he is one of the lucky ones, who was able to find another house that was better value.

At a time when everything from food to petrol to energy is going up, many are being pushed out of the rental market altogether, says Edwina MacDonald.

"Right now we're at this crisis point in the housing, rental and social housing markets," she said.