New Zealand’s next PM: How will they be chosen and when will we know who it is?

New Zealand’s prime minister, Jacinda Ardern, will step down no later than 7 February after her shock resignation on Thursday in which she said she “no longer had enough in the tank” to do the job.

Leadership hopefuls will gather on Sunday when the centre-left Labour party caucus meets to elect a new leader – who will go on to become prime minister. Here’s what will happen:

Who can vote and how?

The 64 Labour members of parliament, known as the caucus, will meet in private at 1pm local time (0000 GMT) on Sunday to elect a new leader. Those who can’t make it can vote by proxy. The winner requires at least two-thirds of the votes, or 43 members.

Leadership hopefuls need seven colleagues to make it on to the ballot: at least 10% of the caucus, excluding themselves. Nominations must be received by 9 am local time on Saturday.

As Labour holds a majority in parliament, whoever they elect will become prime minister, leading the country for a little more than eight months before a general election on 14 October.

Polling over recent months has placed the Ardern-led Labour party slightly behind the opposition National. The most recent polling – taken before Ardern stepped down – suggest that if an election was held today, Labour would lose power.

What if the caucus can’t decide?

They keep going. Multiple votes are allowed, with the lowest polling candidate eliminated each round. The caucus has until 26 January to decide.

If the caucus is unable to pick a new leader by then, the vote will be expanded to include Labour party members and affiliated unions. The caucus vote will be weighted at 40%, party members at 40% and unions at 20%.

Who are the frontrunners?

There are a few. Immigration, police and transport minister Chris Hipkins is a household name for his role leading the government’s Covid-19 response. He declined to rule out running on Thursday.

Transport minister Michael Wood and Minister of Justice Kiri Allan are newer faces in parliament, elected in 2016 and 2017, respectively. If elected Allen would make history as the country’s first Māori prime minister and first openly gay leader

Grant Robertson would have been an obvious frontrunner having managed New Zealand’s finances through the pandemic. He has, however, ruled himself out of the contest. Candidates occasionally become leaders despite this – Ardern herself had said she didn’t want the job shortly before she took it.