Here's how to get on top of your mortgage.

Tightening bank lending is leading to a property crunch in Australia and it could also happen here, a housing commentator says.

Christchurch-based Hugh Pavletich of the housing thinktank Demographia says reports of Sydney and Melbourne houses losing $1000 a week are a result of rising interest rates and the Australian banking inquiry, making banks ultra-cautious.

​Pavletich said that in Australia, the housing bubble was bursting. "The days of high multiple-lending are over".

123rf Sydney and Melbourne make up about half Australia's residential real estate market, so wobbles there affect the rest of Australia.

On Friday an Ernst and Young warned that Australia was facing a property industry downturn not seen for 30 years.

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And the Australian Financial Review reported that a 20 per cent fall in property prices from peak to trough could plunge more than 350,000 Australian households into negative equity.

"Our house prices here in Australia had streaked past anything sensible by way of valuation," Deloitte partner Chris Richardson told the ABC.

"Now, finally gravity has caught up with that stupidity and prices are falling."

ROBYN EDIE/STUFF Hugh Pavletich says New Zealand is not isolated from Australia's woes, given most of our banks are Australian owned.

Pavletich said there was a warning for New Zealand in Australia's woes.

"The banks are also stiffening up here in New Zealand, getting a lot more diligent. The lending isn't as loose here as it used to be, and internationally interest rates are lifting, and New Zealand cannot be isolated from that."

Although the flattening Auckland market has been muted so far, there are already reports of developers and first home buyers finding it hard to get finance.

Pavletich said while the Government's Kiwibuild building programme might help ease some of that pain, the deeper issues over land supply and urban limits were still to be fought.

"I think we're going to see increasing pressure on the Government to deal with land supply and infrastructure financing issues."

Auckland: Big city, high house prices, massive mortgages.

Demographia has consistently maintained that any property which is more than three times the median regional income was unaffordable. Australia and New Zealand are well above those multiples.

Pavletich said predictions by AMP Capital that Sydney and Melbourne prices could fall by up to 15 per cent in two years were probably shy of the mark.

"They've got a long way to go after that."

He said New Zealanders were acutely aware of the risks, with an Ipsos survey in July suggesting that half of Kiwis believed housing was the country's number one issue, a greater problem than poverty, healthcare, crime or the cost of living.