One in five property owners say they will face severe mortgage stress if their monthly home loan repayments are increased, a new survey has found.

The Reserve Bank of Australia (RBA) has flagged that it may soon have to lift the cash rate from the “emergency” level of 3.0 per cent.

Economists say the cash rate could rise to five per cent over the next 18 months, which would lift monthly repayments by $450 a month on an average $340,000 mortgage.

An online survey by the Loan Market Group found that 19 per cent of respondents said any increase in interest rates would push them over the limit.

The survey of 600 respondents found 38 per cent could afford to pay only $250 per month more, while 27 per cent said they would be able to pay up to $500.

Only 16 per cent said they could afford to increase their monthly payment by more than $500.

“It should be a concern to the RBA and to the federal government that 57 per cent of respondents said they can’t afford rates to go up another two percentage points,” Loan Market Group executive director John Kolenda said, releasing the survey results on Thursday.

“It’s not just the RBA that home owners have to worry about.

“There’s a strong likelihood of the major banks lifting variable rates independently.”