New Zealand's government wants to trim "super profits" from land banking which it says is the biggest impediment to housing affordability in Auckland.

The recent drop in the value of the New Zealand dollar against the US currency could have a caught a number of companies off-guard.

If house prices start rising faster, it can require lenders to reduce the proportion of the property value they are prepared to lend, writes David Mayes.

The New Zealand dollar fell to a nine month low as investors concerned about global growth moved to the relative safety of US Treasuries.

Economists say the Reserve Bank's intervention in the foreign exchange market last month was too small to make much difference to the exchange rate.

It could take three to five years to close the gap between housing supply and demand in Auckland, if left to supply measures alone, says Reserve Bank governor Graeme Wheeler.