New Zealand house prices epped up to an unseasonally high volume in July, although there was a pause in the rocketing upward trend for Auckland prices.

Auckland's median house price fell by 2.6 per cent to $NZ735,000 ($A659,607), compared to June, according to the latest figures from the Real Estate Institute of New Zealand.

The number of houses sold in July rose 38 per cent to 8,121 from the same month a year earlier, the highest number for July in 10 years, and driven by a 41 per cent gain in Auckland, with 3,160 sales, according to the REINZ.

While the median Auckland house price was lower than the previous month it was still about 20 per cent higher than a year earlier.

The national median average rose 3.3 per cent in July to $NZ465,000 for an annual increase of 12 per cent.

"The volume of sales has been exceptionally strong for the middle of winter right across New Zealand, with very strong year-on-year sales growth in the top half of the North Island and Central Otago Lakes in particular," REINZ chief executive Colleen Milne said.

"Inventory continues to be a significant problem in Auckland, with less than 10 weeks' supply available, and there is an emerging problem of available properties in Northland and Waikato/Bay of Plenty."

Stripping out Auckland, the REINZ figures show national sales volumes rose 36 per cent in July from a year earlier, while the median price increased just six per cent to $NZ352,000

Sales turnover in Wellington rose 12 per cent to 697 in July, compared with July last year, for a 4.1 per cent increase in the median sales price to $NZ395,750.

Christchurch sales were up 10 per cent for the same period to 574 for a 5.6 per cent increase in median sales price to $NZ430,000 and Dunedin sales were up 9.2 per cent to 155 while the median price gained 5.8 per cent to $NZ285,000.