John Key's national Party had a 50 per cent approval rating ahead of the polls [Reuters]

New Zealand's opposition Labour Party has conceded defeat in general elections, giving the ruling National Party the win and allowing John Key to return as prime minister.

Opposition leader Phil Goff accepted defeat on Saturday by telling his supporters "the people have made their decision and we treat their decision with humility and respect".

The Labour Party had a disastrous night, winning just 27 per cent of the vote with most already counted. Meanwhile, the National Party was on course to win 60 of 121 seats in Parliament.

Though Key's party appeared to be coming up just short of giving him enough votes to govern alone, he will likely find enough support among minor parties to shore up his leadership.

The Green Party, a possible ally, won 11 per cent of the vote, its best showing ever.

Opinion polls before the vote had put the National Party at just over the 50 per cent mark, with the opposition Labour Party at 27 per cent.

Economic issues

Observers say voters have warmed to Key over his handling of both the Christchurch earthquakes and the deadly blast at the Pike River mine in November 2010.

The All Blacks' recent victory on home soil in the Rugby World Cup final has also created a feel good factor in the rugby-mad nation which has played in his favour, they believe.

Economic issues have dominated the campaign, with Key promising to build on policies of the past three years with an emphasis on sparking economic growth by cutting debt, curbing spending, selling state assets and returning to a budget surplus by 2014/15.

Queues were reported at some suburban booths in major cities as fine weather brought out voters.

Key cast his ballot at a school near his Auckland home and said he was taking nothing for granted despite the party's commanding poll lead.

"You feel a combination of excitement and a little bit of nervousness and anticipation," Key told reporters.

Goff held on to hopes that the party would stage a late recovery, saying it was "all up to the voters".