Labour's chief whip Duncan Webb said in a statement on Friday that nominations close at 9 a.m. and to be nominated the candidate must receive support from at least 10% of Labour's members of parliament.
If there is more than one candidate there will be an election Sunday by caucus -- the 64 Labour law makers in parliament. If a candidate is unable to secure two-thirds of the available votes before Thursday, the leadership contest will go to the wider membership.
The winner will become prime minister until the next general election. Ardern, 42, said Thursday she had "no more in the tank" to continue leading the country, and would step down no later than early February and not seek re-election.
(Reporting by Lucy Craymer; Editing by Chizu Nomiyama)
By Lucy Craymer
