An economist says one reason there is such a shortage of houses available to buy is that people are not selling their existing houses when they buy new ones.
Figures released last week showed new listings of houses available for sale fell to their lowest number for a June month in seven years.
Bank of New Zealand chief economist Tony Alexander, who regularly surveys real estate agents, says low interest rates are making it easy for people not to sell.
He says they are starting to come across examples of people, predominantly in Auckland, moving into their second home but keeping their first as an investment property and not putting it on the market.
Mr Alexander says that is making the supply of houses even tighter.
Demand is already rising, with net migration increasing further and further.
He says there is also an element of catch up demand from first home buyers who have put off buying a property since 2008 and investors who had put off investing in the hope prices might fall.
Mr Alexander says another factor is people who have to shift from Auckland for work, or who go overseas, holding onto their property for fear they would not be able to afford to re-enter the city's housing market on their return.