Prime Minister John Key says he potentially supports income-related restrictions on mortgage lending.
Mr Key said increasing supply was still the main issue to dampen the overheated Auckland property market, but the Reserve Bank had some options to address the demand side.
Investors account for about 46 per cent of property transactions in Auckland.
Mr Key, who again resisted labelling the Auckland housing situation a crisis, said the Government had introduced the bright line test to target investors but the Reserve Bank could take further action.
"I think it's one of the issues the Reserve Bank can give some consideration to, because they can target groups, just like they did with their LVR ratios, and they are looking at income ratios, they have the capacity to look at that," Mr Key told Radio New Zealand.
Debt-to-income restrictions are already used in the United Kingdom, where most buyers cannot get a mortgage higher than 4.5 times their annual earnings.
Asked if he would support similar restrictions here, Mr Key said, potentially.
Last week the Reserve Bank left the official cash rate at 2.25 per cent, with Governor Graeme Wheeler flagging rising house prices as a risk to the country's financial stability.
Wheeler said investors could soon be targeted by new loan-to-value lending rules.
He could not give detail on how restrictive any new rules could be.
The loan-to-value ratio (LVR) is the amount of a loan compared with the value of a property. It is calculated by dividing the amount of the loan by the value of the property.
Last November the Reserve Bank tightened LVR rules to rein in Auckland investors, ensuring banks demand 30 per cent deposits for a mortgage secured against an investment property.
Wheeler said work was being done looking at separate income-related restrictions on mortgage lending.
However, any introduction of debt-to-income restrictions would be complex, and LVR changes could come first.