The risks of unsustainable house prices, and worries that prices could fall, are prompting new limits on how many risky mortgages banks can loan.

The Reserve Bank wants only 10 percent of new mortgages to have a deposit of less than 20 percent.

House prices have rocketed up on the back of cheap, low-interest debt, and a lack of housing supply.

KiwiBank's chief economist Jarrod Kerr joins Māni Dunlop on Midday Report.