Auckland house sale prices by the city's biggest real estate agency failed to rise for the first time in half a year and winter, Reserve Bank moves and international economic stability are being cited as causes.

Barfoot & Thompson's average residential sale price in July was $827,359 but by August had dropped to $821,079 and managing director Peter Thompson explained the reasons.

"There were signs that house price increases were cooling in June and July, and August's figures confirmed that winter had contributed to a small price decline last month. With the approach of spring, prices were now at the crossroads with the most likely scenario being that prices will increase modestly in coming months.

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"Factors which have led to record prices being achieved still remain. However, countering this are new Reserve Bank and Government regulations and rules and concerns around world-wide economic stability," he said.

August sales volumes remained relatively strong at 1314, but that too was below the year's high of 1597 in the heated month of March.

"Sales numbers during the month at 1314 were the highest for an August for more than 15 years, and 44.6 per cent higher than in August last year," said Thompson.

The data out this morning from the agency - estimated to sell about 45 per cent of all Auckland residential properties - showed the number of $1 million-plus sales relatively stable at 46 per cent for May, 45.8 per cent for June, 47 per cent for July and 46.5 per cent for August.

More people are now listing properties.

"New listings in August at 2123 were exceptional, and the highest number in any month for more than 10 years. In spite of this, at month end properties on the company's books at 2957 were only modestly higher than July's 2802 and 375 properties sold for in excess of $1 million, the third highest number in a month, while 14.4 per cent of properties sold for under $500,000, in line with the number for previous months," he said.

January $757,319
February $747,521
March $776,729
April $804,282
May $822,148
June $826,474
July $827,359
August $821,079

January 859
February 843
March 1597
April 1070
May 1225
June 1167
July 1388
August 1314
[Source: Barfoot & Thompson]