The New Zealand dollar fell as dairy futures weakened, raising concern about the outlook for the country's largest export commodity.

The kiwi slipped to 75.64 US cents at 8am in Wellington, after touching a high of 76.63 cents about 11pm last night, and from 75.79 cents at 5pm yesterday. The trade-weighted index slipped to 78.96 from 79.03 yesterday, after touching a high of 79.59 overnight.

The kiwi reversed its initial gain overnight as NZX whole milk powder futures declined when trading resumed at 2am this morning. Some 500 tonnes had traded in the first six hours this morning, with little buyer interest. The biggest declines are in June whole milk powder futures, which are down US$230 a tonne to $2,400 a tonne, and July futures which are down $250 a tonne to $2,450 a tonne.

"This sort of weakness in dairy pricing is clearly going to be weighing on the kiwi," said Mark Johnson, OMF senior dealer, foreign exchange. "There's no buying interest being shown, there's only offers. That could be partly due to the fact that it is still early in the morning but there is a distinct lack of buying interest when these things are getting smashed.

"It's another negative for the kiwi that dairy prices are failing to recover from their lows," Johnson said. "That is a key price that the Reserve Bank does follow."

Globally today, traders are awaiting US Federal Reserve Chair Janet Yellen, who is scheduled to speak at the Federal Reserve Bank of San Francisco Conference on "The New Normal for Monetary Policy".

The New Zealand dollar slipped to 96.76 Australian cents from 96.98 cents yesterday, was little changed at 50.97 British pence from 50.92 pence, gained to 69.58 euro cents from 69.04 cents and fell to 90.21 yen from 90.43 yen.