As New Zealanders reel from Jacinda Ardern's shock resignation as prime minister, her Labour party is moving to replace her.

All roads appear to lead to Chris Hipkins, a close ally of Ms Ardern, but no candidates have declared for the role.

Ms Ardern stunned all-comers on Thursday when she announced her imminent departure from the role, citing exhaustion.

"I know what this job takes and I know that I no longer have enough in the tank to do it justice. It's that simple," she said.

Ms Ardern's shock exit was followed by another surprise, with her deputy and assumed successor Grant Robertson ruling himself out of the race.

Labour MPs are considering their positions and holding talks to decide the leadership ahead of a party room vote on Sunday.

As they left Napier on Friday after the Labour party's year-starting retreat, MPs closed ranks behind that process, with few revealing their voting intentions.

Ms Ardern said she wouldn't support a candidate and backed the team to find a consensus.

"I expect them to deliver a result," she said.

"They are very determined to make that decision on Sunday and to get on with the job they've been elected to do.

"The most important thing is that we focus on a process that is swift, that ensures that the team was able to move quickly back to focusing on the issues that matter for New Zealand."

Mr Hipkins agreed consensus was "likely", saying "the team are taking it incredibly seriously".

"We need to select a new leader and then we need to really unite behind the new leader and continue to deliver stable leadership," he said.

Mr Hipkins is well-known nationally for his role as COVID-19 Minister during the most difficult days of the pandemic.

He is a strong parliamentary performer as leader of the house and is considered a safe pair of hands for difficult areas, hence his shift to the police portfolio last year.

Whoever is successful will have nine months to win over the public before a general election.

In her last act as prime minister, Ms Ardern called the next election for October 14.

She also set in train the process to replace her, which begins with the caucus meeting in Wellington on Sunday.

As per party rules, two-thirds of the 64-strong caucus must support a new leader at that meeting or the decision will be thrown to the wider party membership.

Some believe Mr Robertson, the 51-year-old deputy prime minister, would be open to reconsidering if asked. 

"I just told him 'you should do this - you are the person for it'," Wellington-based MP Ibrahim Omer said.

"He's the natural successor but he doesn't want to do it. We have to respect that."

Other possible contenders for the top job include health minister Andrew Little, justice minister Kiritapu Allan and immigration minister Michael Wood.


AAP