The International Monetary Fund (IMF) has suggested the Reserve Bank of New Zealand look at using more macro-prudential tools to slow down Auckland's rampant housing market if the current measures to limit low deposit lending do not work.The IMF said in its annual assessment of the New Zealand economy that the RBNZ could look at increasing capital requirements for housing loans or imposing a formal test for debt serviceability.The RBNZ launched a second round of restrictions on high loan-to-valuation ratio lending on November 1, targeted at slowing lending growth to landlords in Auckland, where annual house price inflation has risen over 20 per cent this year. Landlord loan LVRs are now restricted to 70 per cent in Auckland, down from 80 per cent.The IMF said after meetings with Finance Minister Bill English, RBNZ governor Graeme Wheeler and other officials that the RBNZ could look at introducing tougher measures to slow lending growth to buy the market time while housing supply catches up with demand."The impact of the new measures to reduce financial stability risks will need to be evaluated, but the authorities should be prepared if further steps are needed," the IMF said. "This could include targeted higher risk weights on housing loans, higher down payments, and a formal debt serviceability test," it said.Elsewhere, the IMF said New Zealand's banks remained well capitalised and stress tests indicated they could withstand a sizeable shock to house prices, the terms of trade. "Nonetheless, a period of extremely low liquidity in financial markets or an excessive risk premium required by international investors could call for both monetary and fiscal support," the IMF said."The banking sector continues to face long-standing structural issues related to reliance on offshore funding and a large share of mortgage lending," it added.