Labour leader Jacinda Ardern has acknowledged outgoing Green co-leader Metiria Turei's "enormous contribution", while opponents have said her departure was "inevitable" and damaged the party's brand.

Photo: RNZ / Rebekah Parsons-King

Labour Party leader Jacinda Ardern paid tribute to Mrs Turei's political career.

"I want to acknowledge Metiria's enormous contribution to politics and important causes during the fifteen years she has been in Parliament," she said.

Photo: RNZ / Rebekah Parsons-King

Ms Ardern said the co-leader had always had a steadfast commitment to social justice, championing the rights of children, and changing the government - a challenge she said they would both remain focused on.

National's campaign manager Steven Joyce said Mrs Turei's resignation was inevitable.

"It probably had to happen. I think it's going to cause even more trouble for the Greens.

Photo: RNZ / Rebekah Parsons-King

"There's real mess on the left at the moment, a lot of change is occurring, and I think that will be something people will be weighing up."

New Zealand First leader Winston Peters said Mrs Turei had paid a heavy price for a series of bad mistakes.

Politics was an unforgiving business where people behave like vultures when it comes to someone's demise, he said

Photo: RNZ / Rebekah Parsons-King

"It is tough to see anyone go from here in that way. No one wants that to be their legacy."

ACT Party leader David Seymour said Mrs Turei had done the right thing for the first time in a long time and it was a shame it had taken so long for her to go.

"It seriously damaged their brand. They're a party that marketed themselves as being about the environment and they are in to as dirty a politics as anyone else."

Photo: VNP / Daniela Maoate-Cox

He said she had exploited the people she purported to represent and badly damaged the Greens.

Māori Party co-leader Marama Fox said the pressure was mounting for her to leave.

"It has certainly polarised New Zealand. Either you were with Metiria or you were not. But as things unfolded [her resignation] started to feel inevitable.

"It's sad because Metiria has given so much for the causes she believes in."