New Zealand's most expensive houses are being particularly hard hit by the weak property market, new data suggests.

The Real Estate Institute has released its September data, which showed nationwide house prices as measured by its house price index were up 0.4 percent in the month.

Over three months they were down 0.1 percent, over one year 1.5 percent and they were down 17 percent from the peak.

Wellington prices were still almost 30 percent below the peak and Auckland's about 25 percent, down 4.5 percent and 3.2 percent, respectively, over a year.

But Canterbury was only 0.1 percent below, Southland 0.6 percent and Otago 0.9 percent.

Canterbury values were up 3.1 percent over a year and Otago's 2.8 percent. Southland was up 7.5 percent.

Infometrics principal economist Brad Olsen said there was little sign yet the market had turned a corner.

He said more expensive properties seemed to have been particularly hard hit.

"If you look at sales by price or price group, the house price declines we are seeing at the moment are having a much larger hit to more expensive houses.

"The number of houses worth over $1 million sold in September was down 17 percent from a year ago. The number of houses sold under $500,000 was down just 2.3 percent."

The number of sales nationally was down 11.6 percent in September compared to a year earlier.

Auckland sales were down 13.6 percent month-on-month when seasonally adjusted.

Institute chief executive Lizzy Ryley said buyers were moving when the property, price and timing suited them. "Many vendors recognise that achieving a sale may require patience."

New listings increased 0.8 percent year-on-year and the number of houses available for sale rose 10.7 percent.

"Parts of the country, including the significant market of Auckland, have seen a lot more properties available," Olsen said.

"There is less sales activity coming through. House prices are lower and it's taking longer to buy a property."

He said while places like Canterbury, Otago and Southland were recording stronger house price growth, there were not large numbers of houses being sold.

"It leads through to what we're seeing in terms of properties available for sale on realestate.co.nz.

"If you look at the figures there, there's been seasonally adjusted growth in the number of properties available for seven months in a row now to the highest level since the start of 2015. Those available property numbers are now 11 percent higher than a year ago, and there's half a year's worth of sales sitting on the market."

Westpac chief economist Kelly Eckhold said the numbers looked weak.

He said the "days to sell" measure of 47 to 48 days was longer than would normally be required to see regular monthly price growth.

"That's one of the reasons why we revised down our house price forecasts a couple of days ago … the combination of falling prices, but also falling sales nationally as well."

He now expected house values to fall 1.4 percent over the year and for the market not to improve until the middle of next year. Westpac expected growth in prices of 1.75 percent next year.

"This is a cycle that doesn't seem to be being driven by increasing house prices driving increased household wealth and therefore consumption and associated residential investment. The cycle we're seeing here is very much more driven by the external sector, the agricultural and export sector and the tourism sector in particular are carrying a disproportionate amount of the load in terms of bringing the economy forward."

He said while Southland and Canterbury appeared stronger, Wellington was volatile.

Institute chief corporate affairs officer Trey Sarten said consumer confidence would be key to get slow markets moving again.