Australia's wealthiest suburbs are among the most vulnerable postcodes in terms of mortgage stress.

Private data compiled by Digital Finance Analytics has captured 16,000 homes within 20 suburbs that are under significant financial strain.

For example, households in Melbourne's Toorak, where the median house price is $3.5 million, are five times more likely to default on mortgage payments than the national average.

Residents in the Sydney beachside suburb of Bondi are facing the same financial stress.

"Quite a few households are actually cash strapped, despite the fact that they're affluent ... and that's a really quite unusual phenomenon," said Martin North, founding principal of Digital Finance Analytics.

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The analysis shows the extent to which wealthier households manage their finances over the next 12 months will be the acid test of whether Australia experiences a property crisis.

Mr North said these households - while currently enjoying the spoils of a once-in-a-generation house price boom - will be "disproportionately affected by even a small rate rise".

On Sydney's leafy north shore, in suburbs such as Hornsby and Gordon, home owners are already making late mortgage repayments.

"If you're a more affluent household, you'll tend to have higher costs," Mr North observed.

"You'll be going out and eating more, you've got bigger cash flow issues with regards to credit cards, say larger credit cards, and larger repayments on the credit cards, you have a more expensive car.

"So this is about lifestyle."

Next 18 months the 'acid test' for a 'property crisis'

The data also showed the probability of households in the riskiest 20 suburbs defaulting on mortgage repayments over the next 12 months ranged from about 3 to 5 per cent. A probability of more than 2 per cent is "significant", Mr North said.

Velocity Trade financial expert, Brett LeMesurier, said it is wealthier Australians with multiple properties that will be hit hardest by any interest rate rises, including independent moves beyond Reserve Bank decisions.

"Because that's where the banks have shown that they at the end of last year shown that they would target that's their preferred method of maintaining their margin, [targeting investor loans]," he told ABC news.

Mr North said if interest rates do rise, a growing proportion of households will be under pressure.

"These are the early warning signs of potential difficulties," he said.

"So how households will respond over the next 12 to 18 months, and how lenders respond and how regulators respond in a potentially rising market, is going to be the acid test of whether we end up with a property crisis, or whether we muddle our way through."