The number of houses listed for sale in Auckland dropped to its lowest number in 20 years at the end of December, the city's biggest real estate agency says.

Barfoot and Thompson has released its figures for the month, saying the 796 sales in December was 19.3 per cent lower than sales in November and the lowest in any month for the past 22 months.

The average sale price of $NZ869,492 ($A814,360) was down only 0.8 per cent on November's record average price while the median price rose 0.6 per cent to an all-time high of $NZ800,000.
"Sales data for the final month of the year is sending mixed messages as to where the market will head in 2016," said managing director Peter Thompson.

The factor most likely to affect January sales was the extremely low number of listings at the end of December which, at 2431, was down 25.2 per cent on November, and the lowest number for any month for more than 20 years, he said.

"With a growing population and the number of new builds failing to keep pace with demand, competition for properties is likely to remain strong in the first quarter of 2016."

January sales were always influenced by the summer holidays February's sales data - available in mid-March - would paint a clearer picture for the year.

The Reserve Bank has identified the heated Auckland property market as one of the biggest risks facing the country's lenders, along with a slump in dairy prices.

DECEMBER STILL EXPENSIVE IN AUCKLAND:

* 278 properties sold for in excess of $NZ1 million
* 202 for in excess of $NZ750,000.
* 44, or 5.5 per cent, sold for less than $NZ500,000.
* In 2015, the average sale price was $NZ817,096, an increase of 14 per cent on 2014
* In 2015, the median price was $NZ755,333, 17.4 per cent higher than 2014.