Phil Goff has announced he will resign as Labour Party leader on December 13.
Candidates - including MPs David Cunliffe, David Parker, David Shearer, Grant Robertson and Nanaia Mahuta - are in the fight to take his place.
In an address from Parliament this afternoon, Mr Goff said he would be moving to a back bench role in Parliament in the wake of Labour's crushing election defeat to National.
His deputy leader Annette King will also resign.
Mr Goff said his departure was the first step in rebuilding the flagging Labour Party fortunes.
"I believe the Labour Party can and will fight back."
Mr Cunliffe and Mr Parker are believed to be the frontrunners to take Mr Goff's position as leader.
He named them among a crop of potential leaders, but said election campaign manager Grant Robertson, Hauraki-Waikato MP Nanaia Mahuta and rising star David Shearer had also put their hats in the ring.
The incoming leadership would be in discussions with their caucus colleagues over the coming weeks in an effort to gain their support, Mr Goff said.
"It's on two people that can lead us forward into the future that are strong candidates to be Prime Minister and Deputy Prime Minister."
Mr Goff would not reveal who he was supporting in the leadership battle.
While he said he had no problem with potential Labour leaders using the media to talk up their strengths, the eventual vote on his replacement would be private.
"I'm going to listen very carefully to what the candidates have to say to me. But in the end it'll be like a ballot box."
He was looking forward to working 60 hours a week, after putting in 80 to 100 hours as leader.
Earlier today, Newstalk ZB reported party numbers appear to be fairly evenly split between David Cunliffe and David Parker but the party's old guard are lobbying hard for Mr Parker to succeed Mr Goff.
They believe Mr Cunliffe was disloyal to Mr Goff and doesn't deserve to take over from him.
It's understood senior jobs are being offered to those in the Cunliffe camp in an attempt to secure their support for Mr Parker.
Jones: Labour must reconnect with Maori
Meanwhile a slightly emotional Labour MP Shane Jones believed the party needed to reconnect with Maori.
Speaking before today's meeting, Jones said he wasn't standing for the leadership
"because I know how to count".
"Look at the six or seven people who are no longer back. They were all friends of mine. I went to St Stephens' School and one thing I learned there was how to count."
Mr Jones said he was "personally pained" that Kelvin Davis had not made it back in because his list place was below the cut off for Labour's 27 per cent vote. He had recruited Mr Davis into Parliament in 2008. He was also upset that former MPs such as Stuart Nash and Carmel Sepuloni had not made it back.
He said Labour's bad result should not be seen as "a minor aberration" and he believed it would take some time to figure out how to resolve it.
"Really we've got to delve deeply into why three out of every four New Zealanders who cast a vote said we were unsound and unfit to govern. I don't think that will change until we deeply address those challenges. Until we really understand why so many people moved away from us, then we are going to be where we are for a long time to come."
Before the meeting Mr Parker said he was not denying he would put his name forward.
Mr Cunliffe said he had been sounding out his colleagues and the response was "encouraging."
He said the party needed to reconnect with its base after getting its lowest election result since the 1920s but would not comment on whether he believed he was the person to do that until after Goff's announcement.
"I want to honour Phil Goff and the role he's played. He's been energetic and true to Labour's values."
He expected the process around the leadership to be "robust."
Asked about a whispering campaign against him, including claims he had not supported Goff well, he said he believed the public would see through it.
"I'm not going to respond in kind. That's clearly people positioning for whatever comes after today. It's nonsense and you can take it with a big grain of salt."