New Zealand's financial regulator is probing two possible cases of insider trading and market manipulation, after receiving 15 complaints about such behaviour in the past year.

Reserve Bank Governor Graeme Wheeler says the NZ dollar is susceptible to a "significant downward adjustment," in a statement issued today.

Last month's trade deficit was an unexpectedly small $472 million as imports exceeded exports by 13 per cent.

New Zealand posted a narrower trade deficit in August as exports of live animals and dairy products rise and imports from major trading partners declined.

The dollar declined on concern about slowing growth in China and after Fonterra cut its forecast payout to farmers.

Shares in Chinese baby-milk maker Beingmate Baby & Child have rallied sharply since Fonterra entered an alliance with the firm, which includes the Kiwi dairy giant buying a 20 per cent stake in its new partner.

Saudi Arabia will need to keep cutting oil output to sustain prices above $100 a barrel as global oil demand weakens, analysts say.

The NZ economy grew just ahead of expectations in the second three months of the year, with the fastest growth in the services sector for seven-and-a-half years.

The Kiwi dollar dropped to a seven-month low after the US Fed raised its expectation for the level of interest rates by the end of next year.

The gap between what New Zealand earns from the rest of the world through trade and investment and what it pays widened in the June quarter as falling dairy exports started to weigh on the trade balance.

NZ's current account deficit rose by $1.4b in the past three months reflecting falling dairy prices and a large revision to investment flows into the country.

The dollar held below 82 US cents overnight after the Reserve Bank yesterday reiterated that is too high and signalled interest rates would remain on hold.

Interest rates have been held at 3.5pc as Graeme Wheeler signals he won't be as aggressive with future hikes.

The NZ dollar declined as investors gain confidence about a recovery in the US economy, increasing demand for the US dollar.