Australians are the biggest sector of overseas buyers in the New Zealand housing market - but they are also selling up large.
A BNZ-Real Estate Institute survey suggests 8% to 9% of houses are being sold to people living abroad.
Real estate agents report that about 22% of overseas buyers, and vendors, are Australian, 20% of are Chinese and 13% are from Britain.
BNZ chief economist Tony Alexander said more data is needed on ways to cool housing demand, such as whether to impose a tax on overseas buyers.
He estimates half the overseas buyers are either immigrants buying before they move here, or New Zealanders returning home - especially from Australia and the United Kingdom.
But, he said, housing prices will continue to rise without steps being taken to encourage new house building.
Mr Alexander said results from this year's Census will indicate how many houses are empty, possibly because they are being bought speculatively from abroad or not being sold when people return to their home country.