Analysis: Jacinda Ardern's resignation announcement has changed the political landscape

Analysis - Jacinda Ardern's resignation announcement has turned politics on its head and Labour must now find a new leader capable of taking on the task of regaining the lead over National - an awesome undertaking in an election year.

The term "bombshell announcement" is often over-used but not this time - Jacinda Ardern's decision to resign was totally unexpected and the blast zone covers the political landscape.

She admitted her caucus was "surprised" and that was probably an understatement. For more than five years Ardern has been the most popular prime minister in the polls and often described as Labour's best chance of winning a third term for Labour.

This seemed so sure that there's been little speculation about who would take over if she left - and the most obvious successor, her deputy Grant Robertson, has said he isn't in the running.

Over the next 24 hours the candidates will emerge and caucus will vote on Sunday. That's not much time for gathering support and counting votes, and perhaps that's intentional. Labour doesn't need an untidy scrap, it needs consensus and quickly.

Frontrunners will soon be visible, and among them are likely to be Transport Minister Michael Wood and Education and Police Minister Chris Hipkins.

Wood is one of Ardern's most competent cabinet ministers, a good speaker with a solid Labour background. Hipkins is a highly experienced cabinet minister and is well known to the public from the time he was in charge of the response to Covid-19.

Neither was immediately prepared to say they wanted the job, but neither ruled out standing.

Stuff suggests Megan Woods, Kiri Allan and Nanaia Mahuta could be contenders, but it's difficult to see any one of them gaining more support than either Hipkins or Wood.

The Herald's Audrey Young said the best option would be for Robertson to change his mind and give the finance portfolio to Hipkins or Megan Woods.

If that doesn't happen she thought Hipkins was the best bet.

"If he puts his hand up for the Labour vote on Sunday he should have no competition," Young said.

At her press conference Ardern was asked whether she was effectively handing the election to National and she replied - of course - that she wasn't and believed a new leader could take her party to victory.

That really does seem a long shot. There isn't going to be anyone able to spark the enthusiasm of Jacindamania that saved Labour in 2017, and whoever it is will have to start from the beginning with the voters.

Labour ended last year behind in the polls, with a solid trend showing National and ACT would be able to form a government.

When governments are behind in the polls it's extremely difficult for them to turn that around, and Labour is in no position to be able to offer enticing policies that would inevitably mean spending money that would fuel inflation.

Add to that the imminent end to the petrol excise cut, big increases in the cost of mortgage repayments and an economic recession if the Reserve Bank's warning becomes reality, and the enormity of the task facing Labour's new leader starts to look truly daunting.

National's leader, Christopher Luxon, must be relieved and thankful he isn't going to have to take her on.

Until Ardern's announcement it had been considered that one of Luxon's most difficult tasks was going to be debating Ardern in the run-up to the election. He's a relative newbie, he's been inclined to be gaffe-prone, he's not lighting fast on his feet and could have risked being taken apart.

That's not going to happen now. Whoever leads Labour into the election is going to have less leadership experience than Luxon. In that respect, and it's an important one, the playing field has been levelled.

*Peter Wilson is a life member of Parliament's press gallery, 22 years as NZPA's political editor and seven as parliamentary bureau chief for NZ Newswire.