Some of the government's most contentious portfolios will soon have a fresh face after the prime minister's first cabinet reshuffle.

The ministers who overhauled the health system and ushered in the Three Waters reforms were demoted in the shake-up.

Andrew Little lost the health portfolio and picked up defence while Nanaia Mahuta no longer has local government.

First term MP and former physician Dr Ayesha Verrall is now set to replace Little as Health Minister; a role she says she knows will be difficult.

"I'm under no illusions that health is a tough portfolio but I think that I'm gonna bring the same enthusiasm I always have to making improvements for the health of New Zealanders."

Joining Little on the slide down the rankings is Nanaia Mahuta, who had shouldered the bulk of the criticism about the government's agenda to reform water management.

Te Paati Māori co-leader Debbie Ngarewa-Packer says she's disappointed to see the demotion and says Mahuta did everything she was asked to do in the face of fierce criticism.

"It wasn't just Jacinda [Ardern] that was at the revolting end of some racist and misogynistic abuse and I guess that's her reward for being committed and loyal and honourable to her party."

Wairarapa MP Kieran McAnulty is taking up the role of local government minister, after holding the associate role since last year, and was moved into cabinet in the reshuffle.

In a statement, Mahuta says the role is in excellent hands with McAnulty, who has shown an ability to bring a rural perspective across the sector.

While the prime minister had ruled out fully scrapping the Three Waters reforms, it was possible some changes would be made in the coming weeks and months.

"We're going to take a close look at the Three Waters reforms; certainly leaving open the possibility of a reset there," Hipkins says.

The PM ringfenced himself, his deputy Carmel Sepuloni, Kelvin Davis, Grant Robertson and Megan Woods as Labour's front bench.

Robertson remains the minister of finance, while Michael Wood now has an associate finance role and an entirely new portfolio - as minister for Auckland.

A lifelong Aucklander, Wood says the new role is more important than ever as the supercity navigates and recovers from this week's deadly floods.

"We need to make sure that we have a singular focus and point of accountability so that we can work with local government, business leaders, workers and community leaders to make sure Auckland pulls through this difficult period."

Labour list MP Jan Tinetti is made the new Education Minister while Phil Twyford - who has been a minister outside cabinet - wi dropped from the executive altogether.

MPs Ginny Andersen and Barbara Edmonds have been moved straight into cabinet, while Willow-Jean Prime, Duncan Webb, Rino Tirikatene and Deborah Russell were made ministers outside cabinet.

National's Christopher Luxon says it doesn't matter who came in, as the top five ministers under former prime minister Jacinda Ardern have been retained.

"When you look at the whole cabinet in its entirety it really is the same players that have been there for the last five and a half years, delivering worse outcomes for New Zealanders."

The cabinet reshuffle was formalised by swearing-in ceremonies at Government House this morning.

-Anneke Smith/RNZ.