After a year of successive interest rate rises, the proportion of Australian mortgage owners deemed 'at risk' has surpassed previous records, with one in five now 'extremely at risk', new research shows.

Mortgage holders are considered 'at risk' if mortgage repayments exceed 25-45 per cent of after-tax household income. More than 640,000 households are currently in this zone.

Research by Roy Morgan predicts this proportion will be even higher if the Reserve Bank of Australia (RBA) raises interest rates again.

Roy Morgan chief executive Michele Levine compared the current level of "risk" to that during the global financial crisis. Further interest rate rises will cause these figures to soar further, she said.

"The decline in CPI so far in 2023 has led many to believe that the RBA may have completed its rate hiking cycle after raising rates in June. However, while the fall in quarterly CPI figures is welcome, there are still fresh inflationary pressures in the economy," Ms Levine said.

Rising energy and petrol prices have been a concern for inflation, with petrol prices rising for the first time since July 2022 to more than two dollars a litre. Ms Levine warned that the RBA's rate hikes may not be over yet.

"While many believe the RBA has ended its rate hiking cycle, inflation has been exacerbated by the low Australian dollar and high petrol and energy prices, which could force the RBA to raise rates further in the coming months," she said.

Unemployment is seen as the factor with the biggest impact on income and mortgage pressures. One in five Australian workers is either unemployed or underemployed. in July, Australia's unemployment rate fell 1.2 per cent, but underemployment has risen to 9.5 per cent.

If unemployment rises sharply, pressure on mortgages is bound to increase, reaching a record high of 35.6 per cent of mortgage holders considered 'at risk' in May 2008 during the global financial crisis, Ms Levine said.

Roy Morgan modelled the impact of two potential RBA interest rate hikes on 'mortgage stress' and showed that 108,000 mortgage holders would be 'at risk' if the RBA raised interest rates by 0.25 per cent twice, in September and October.