Auckland house prices are running hot but in parts of Australia's biggest city the market is something else.

Doctors Andrew Hardy and Alex Bereny bagged a 900 per cent return after offloading their property in Sydney's Double Bay, which housed their medical practice, on Monday.

They bought the five-bedroom house in 2004 for A$475,000, the Australian Financial Review reported.

It sold at auction for A$4.6 million ($4.9m), an almost 10-fold increase on the purchase price.

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The AFR reports that the final price for the 582 sq m property, which was purchased by a private investor, came in well above the price guide of A$3.8m to A$4.1m.

As of mid-September, Sydney house values had risen 5.3 per cent quarter-on-quarter, according to CoreLogic figures.

Property prices in Australia's biggest city have been gathering steam this year - thanks to low interest rates and a resurgence of investors - after a cooling off in late 2015 and early 2016.

The median house value in Sydney briefly dropped below A$1 million earlier this year, but it was back above that level in the June quarter.

The average Auckland house price broke through the $1 million mark in August.