Wellington mayor Tory Whanau has announced she is no longer running for a second term, a move which took one of her biggest would-be opponents by surprise.

Whanau, who won the mayoralty in 2022 as an independent and had secured the Green Party's backing for re-election, has now changed her tune, saying she did not want a Green vs Labour battle.

On Monday night, former Labour MP Andrew Little confirmed he had Labour's backing to contest the mayoralty.

Whanau said when she had put her name forward to run for mayor again, she was worried there were no viable candidates, but Little's entering the race had "changed the game" and she wanted to focus on what was important to her.

"I have a lot of respect for Andrew and his leadership skills. He has support from many corners and the skills and experience to unite our council. The progressive goals I have fought for are at risk this election and I do not want a Green vs Labour narrative to distract from what's important for our city. That is not what this election should be about," she said.

Whanau said she would instead run for the council's Māori Ward, and support other Green candidates to be elected to the council.

"I want to continue making Pōneke a city that embraces Te Tiriti, work closely with mana whenua and deliver on affordable housing, nature and water."

Whanau had just launched the start of the Golden Mile Courtenay Place precinct upgrade, and said it was a key milestone for her mayoralty and the "transformative change" she campaigned on.

She said she was also proud of the council's $1.8b investment in water, the passing of the district plan, 27km of new cycleways and 8km of bus priority lanes, the planting of 223,000 trees, work to switch the pool network from fossil fuel heating to renewables, a boost to funding city safety and tackling homelessness, and funding the City Mission to open New Zealand's first wet house.

She said the council was also on track to complete the Moa Point waste minimisation plant, Te Matapihi/Central Library and Town Hall re-openings, the completion of Te Ngākau Civic Square and the regeneration of Courtenay Place.

Whanau had also previously been open about how she considered quitting the mayoralty after facing scrutiny for her political and personal challenges.

The government had appointed a Crown observer to the council, who observed the council faced challenges similar to many others around the country, although noted it would have been possible for the council to sign off on its long term plan, and decide later to sell or keep its 34 percent stake in the airport.

"Change isn't easy and will always have its critics. But I have stayed true to the vision I was elected to deliver and always been upfront about the challenges we face," Whanau said.

Whanau's exit means Little will now go up against current councillor Ray Chung, former councillor Rob Goulden, conservationist Kelvin Hastie, businessman Karl Tiefenbacher and Wellington Live's Graham Bloxham.

Little, who was confirmed at a Wellington Labour Local Body Committee on Monday evening, said he was honoured to receive Labour's backing.

"I intend to run a people-powered volunteer campaign involving tens of thousands of door knocks, phone calls and deliveries. The support of local Labour volunteers will be invaluable as we build our campaign network," he said.

Right-leaning independent mayoral candidate and current Wellington councillor, Ray Chung, told Morning Report he wasn't surprised by Whanau's decision.

Chung said he was still "very confident" in his chances.

Wellington challenges

In a statement, Little credited Whanau for getting on with the job in the face of online abuse.

"I also want to say that while criticism of public leaders is healthy and necessary in a democracy, at times during Tory's mayoralty this has crossed a line into personal abuse, particularly in online spaces.

"This sort of abuse discourages good people from standing for public office and it needs to stop."

Wellington faced significant challenges that required urgent attention, he said. "From infrastructure issues to housing affordability and unaffordable rates increases, there's a growing consensus that we need a new direction."

He called on those who supported Whanau to back him.

Speaking to RNZ's Morning Report on Tuesday, Little said he had been approached by people across the political spectrum to run, including some from Whanau's Green Party.

"That's what persuaded me that I thought I had something to offer, and now is a good time for me.

"Since I've announced, I've continued to have support expressed to me from right across the political spectrum. So I was confident from the outset that this was totally winnable for me."

He said Whanau rang him last week and told him of her exit, which was a "wee bit" of a surprise.

"I thanked her for letting me know and I wished her well… I mean, she had committed to campaigning for the mayoralty for a second term, and I thought that this was going to be a contest with multiple contestants.

"But anyway, she's made a decision. I accept that, I acknowledge what she's done in the time she's been there, but I think the city is looking for new leadership and I put myself forward for that reason."

Little said he had respect for the other candidates, which included Graham Bloxham, Ray Chung, Rob Goulden, Kevin Hastie and Karl Tiefenbacher.

Little is endorsed by Labour but how he chooses to run his campaign is up to him, Labour leader Chris Hipkins told Morning Report.

"I think he'll be a fantastic mayor of Wellington."

Photo: RNZ / Samuel Rillstone

Whanau's announcement came literally the morning after work on the controversial Golden Mile project got underway. Little said he was "not in the business of ripping up contracts", but said future work on the project could be slowed.

"Business conditions in the CBD are pretty fragile, and the Golden Mile may well be a good idea may well come to fruition.

"The question is whether we have to do it all sort of straight away, or whether we do look to just getting through what has been a very difficult time for Wellington City at the moment, get some confidence back in our business community, get people back in the city, and then we can sort of proceed from there."