NZ Labour confronts life without Ardern

New Zealanders, still reeling from Jacinda Ardern's shock resignation, may know her replacement as prime minister on Saturday morning.

New Zealand Labour is closing nominations for her replacement at 9am on Saturday.

If there is only one candidate - and all roads appear to be leading to Chris Hipkins - then he will be announced as such and confirmed at a partyroom meeting on Sunday.

If there is more than one, then that caucus meeting will serve as a showdown to become New Zealand's next leader.

However, from the outgoing prime minister down, Labour MPs appear determined to resolve the matter swiftly and present a united front to Kiwis.

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.

The announcements have scrambled Labour's senior MPs, who have held backroom talks among themselves to decide on a pathway forward.

Ms Ardern said she wouldn't support a candidate but urged them to find a consensus on Sunday.

"I expect them to deliver a result," she said from Hawke's Bay Airport as she left Napier, the site of her bombshell announcement.

"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."

If MPs cannot decide on a candidate on Sunday, the vote will go to grassroots members.

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 will culminate at 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.