Labour leader David Shearer has stepped aside.
Shearer said his resignation would be effective once a new leader was elected.
Whip Chris Hipkins said a replacement would be decided in three to four weeks.
Shearer said he had informed party president Moira Coatsworth and secretary Tim Barnett this morning.
''We need to do more and we haven't had the lift [we want],'' he said.
He did not think he had the support of his full caucus.
''To really take the country forward we need a Labour government,'' he said.
"The ambitions of one person should never be larger than that greater purpose."
Whoever became leader would have his full support, he said.
Shearer said it had been a privilege to lead the party for the past 20 months.
''But we do need to do more, so the time has come for me to hand over to a new leader who can take Labour through to 2014."
He said there was no letter of ultimatum and there was no vote.
"But from the soundings I have taken from colleagues, I realise I no longer enjoy the confidence of a number of my caucus colleagues," he said.
Labour MP Lianne Dalziel, who has quit the Christchurch East seat to pursue the Christchurch mayoralty, said the announcement was "sad".
"It is always sad. I have always had a tremendous admiration for what he understood about what we were going through in Christchurch,'' she said.
"I remember I had him down here before he was party leader for a recovery meeting in New Brighton. He said how impressed he was with the way the community was taking charge.
''I have always had a belief in what he has to offer."
Shearer has been dogged by bad polls and a stunt with dead fish backfired on him in Parliament this week.
He was chosen as Labour leader in December 2011, in a two-man contest with David Cunliffe.
He took over from Phil Goff, who resigned following election defeat to National.
Shearer had entered Parliament in 2009 - after Helen Clark quit to take up the top job at the UNDP - winning the Mt Albert by-election with a majority of 9718.
It is unclear who would replace Shearer if he goes.
Under Labour's rules, there would be a run-off for the leadership with the party having 40 per cent of the vote, the caucus having 40 per cent and affiliates, including unions, 20 per cent.
- © Fairfax NZ News
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