New Zealand's prime minister has called a general election for November 8.

Helen Clark is hoping to extend her nine-years in office despite being dogged by economic recession and political scandal.

Her Labour-led coalition, which has been in power since 1999, has trailed the centre-right National party in opinion polls for the past year.

"This election is about trust," Clark, who had to call elections by November 15, told a news conference on Friday.

"It is about which leader and which major party we New Zealanders trust our families' and our country's future with."

The opposition National party leader, John Key, says it is time for a change of government.

Under Clark, Labour has been active in international affairs, sending troops to fight in Afghanistan and keep the peace in East Timor, as well as sending engineers to Iraq to rebuild war damage, although she disagreed with the US-led invasion.

The main issues in the election appear to be the economy and climate change, although a scandal involving a former minister could also be a factor.

Winston Peters, the leader of the New Zealand First party which forms part of Clark's coalition, stepped down last month as foreign minister pending the outcome of parliamentary and police inquiries into donations made to his party by a wealthy businessman.

Clark has distanced herself from Peters but the inquiries could prove detrimental to her campaign.