Auckland's largest real estate agency says prices have shot up, driven by low interest rates and a lack of listings.
Barfoot and Thompson says prices reached an all-time high in June, averaging $589,000, an increase of 1.2% compared with the previous month, and 8.5% higher than the same period last year.
Barfoot chief executive Wendy Alexander says demand remains extremely buoyant.
Ms Alexander says Barfoot and Thompson sold 994 properties during the month, the highest number for June in five years.
Meanwhile, the number of houses on the agency's books has dropped to 4078,the lowest total in nearly seven years.
Eighty-four homes sold for more than $1 million.
Goldman Sachs economist Philip Borkin says more homeowners are likely to start selling up if prices remain high.
He says builders and developers will also be taking heed of the trends but remain cautious.