Labour list MP Shane Jones has joined Labour deputy leader Grant Robertson in saying he wants to be leader of the party.
Grant Robertson was the first to announce he is seeking the leadership, following David Shearer's decision to stand down on Thursday.
Earlier, Shane Jones said it was "very unlikely" he would stand.
Nominations close for the leadership at 10pm on Monday, with the contenders to be announced on Tuesday.
David Cunliffe has yet to declare, but is expected to announce today he'll run.
Otago University’s Bryce Edwards told RadioLIVE he believes Cunliffe is the stronger candidate, and Mr Robertson may be seen as too much of a political insider.
"Outside of the so-called Wellington beltway, he's not that well known. He's seen as someone who does deals that are behind the scenes. Not exactly a man of the people in the way many see David Cunliffe."
Andrew Little and Jacinda Ardern have said they will not be standing.
Under new rules the caucus has 40 per cent of the vote, members 40 per cent, and union affiliates 20 per cent.
Mr Robertson said on Sunday he offered a new generation of leadership that would unify the party to victory in 2014.
"I have taken this decision because I believe I can lead a party and a government that is principled, has vision and works with New Zealanders to give them hope and opportunity."
A TVNZ Colmar Brunton poll released on Sunday found 29 per cent of people think Mr Cunliffe is the best MP to lead Labour.
Mr Robertson was backed by 10 per cent, Ms Ardern 15, Mr Jones 11 and Mr Little 9.
The poll of 500 eligible voters has a margin of error of 4.4 per cent.
NZN / RadioLIVE