New Zealand PM calls September 20 election

New Zealand Prime Minister John Key today called a general election for September 20, when his centre-right government will seek a third term in office on a platform of strong economic management.

The popular Key said he wanted to give New Zealanders plenty of notice about when the vote would take place.

He told reporters his National party "will be campaigning strongly on its record in government and plans to continue the good progress New Zealand is making".

An opinion poll last month gave Key's National party 51 per cent of the vote, with the centre-left Labour Party on 34 per cent and the Greens on eight.

But the former investment banker stressed: "We will be taking nothing for granted.

"I always think elections are like World Cups, they look easy to win but they're actually very difficult, they can be very complex and can have different outcomes to what people think."

New Zealand's complex proportional voting system means it could be weeks after the September 20 poll before a clear winner emerges.

Key said his government would campaign to provide more of the steady leadership that helped New Zealand recover from the global financial crisis and the devastating Christchurch earthquake of 2011.

"As a country, we've been dealing with economic shocks and earthquakes on top of inherited fiscal deficits," he said.

"Working together we are rebuilding Christchurch, our economy and our finances. New Zealand is now heading in the right direction again - I'm proud of the work we've done."

New Zealand's economy is enjoying a healthy recovery from the 2008 global financial crisis, with analysts tipping growth of 3.5 per cent this year thanks to a strong pick-up in dairy exports.

However, with inflation rising on the back of huge construction spending in quake-hit Christchurch, analysts expect the central bank to hike interest rates soon from their record-low level of 2.5 per cent.

The last election was held in November 2011 but Key said he opted for a September date so the poll did not clash with a November G20 leaders' summit in Australia, to which New Zealand has been invited.

Labour leader David Cunliffe, who took on the role in September last year after bitter in-fighting within his party, said his message to Key was "bring it on".

"We are ready, we are up for this. It's game on," he told reporters.

"We're already in campaign mode and we're aiming to give New Zealanders an opportunity for a new beginning.