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.

An air of optimism about the US economy has put the skids under the New Zealand dollar and a drop below US78c could herald further falls, market strategists said.

The most difficult aspect of the Reserve Bank's dilemma is that the longer interest rates stay low.

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

The OECD is urging New Zealand to adopt a deposit insurance scheme to limit depositors' losses in the event of a bank failure.

The Reserve Bank Governor Graeme Wheeler said the central bank had intervened in the currency market to take on the high New Zealand dollar in recent months and was prepared to "scale up" its activities if necessary.

The New Zealand dollar surged to its highest in four and a half years against its Australian counterpart as New Zealand's rising interest rates and growth outlook increase the lure of the nation's currency.