More home owners put up "for sale" signs in May, lured by the prospects of a gradually improving property market.
Real estate.co.nz's latest property report shows the average nationwide asking price rose 3% to $435,887 in May, 4% than the corresponding month in 2011.
After a sharp fall in April, new listings surged 14% to 11,500, which is 17% higher than at the same time a year ago.
Real estate.co.nz chief executive Alistair Helm says the unseasonable pick-up in listings is probably due to sellers becoming more confident about the property market's prospects.
Mr Helm says the influx has helped to boost the inventory of homes available for sale, but Auckland and Canterbury are still experiencing significant shortages.
Earlier this week, the Real Estate Institute downplayed speculation that a housing bubble is building, backing the Reserve Bank's view that there is little sign of house price inflation.