The Prime Minister admits her former police minister had lost "focus" in the portfolio amid rising gang tensions as she announced several major changes today to Cabinet positions.

But National, which has been increasingly putting pressure on Poto Williams and even last week called for her to be dropped, says appointing Chris Hipkins to the role will "not be enough on its own".

Today's Cabinet reshuffle came as Immigration, Broadcasting and Justice Minister Kris Faafoi announced he was resigning, alongside Speaker Trevor Mallard, who will be taking on a diplomatic role in Europe.

In announcing the new Police Minister, Jacinda Ardern also said the "context" in policing had changed significantly in the past 18 months since Williams, with a background in fighting family and sexual violence, was given the portfolio after the 2020 election.

In 2020 the police murder of George Floyd in the United States saw calls to "defund" and ultimately reform police culture sweep the globe.

Prime Minister Jacinda Ardern. Photo / Mark Mitchell

Here, this saw mass criticism over the Armed Response Trials, which predominantly focused on Māori and Pasifika communities despite being sparked by the Christchurch white supremacist terrorist.

"There was some controversy around some of the proposals around [the Armed Offenders Squad] and some concerns around the culture change programme," Ardern said.

"Minister Williams at that time in my mind was the right fit. The focus has changed and with it we've changed the ministerial lineup."

Ardern said she and Williams, who stays in Cabinet as Conservation and Disabilities Minister, "both agreed" the focus on what was needed for police now had been lost.

"It's critical that our focus and time is on supporting the police and implementing our record investment in the front line, passing our further gun law reforms and developing additional measures to deal with the current escalation in gang tensions and violence.

"That focus currently has been lost. Poto is a capable minister and retains my confidence. That's why she is still in Cabinet."

A spokeswoman for Poto Williams said she was unavailable for an interview with the Herald.

National Party leader Christopher Luxon last week called for Williams to be stripped of the portfolio.

He said her replacement was an "acknowledgement of a lack of leadership at a time when violent crime and gang activity are on the increase".

"A change in minister will not be enough on its own.

"What police need is leadership from the Government and powers to confront New Zealand's growing problem with violent crime."

His party on Saturday unveiled a policy package to tackle rising gang membership and violence, including banning wearing patches and assembly in public spaces.

Ardern criticised the ideas as "reactionary" and sociologist Dr Jarrod Gilbert told Newstalk ZB he didn't think the policies had any evidential basis and rather what was needed was "good hard policing".

The changes to Cabinet were largely sparked by departures announced yesterday in Faafoi and Mallard.

Faafoi had wanted to resign at the last election but Ardern had convinced him to stay on, taking on portfolios undergoing major reform in broadcasting and immigration.

He has faced intense scrutiny in the immigration sector including around split migrant families and pathways to residency, while also delivering major reforms.

Departing Minister Kris Faafoi. Photo / Mark Mitchell

He told media his decision had nothing to do with those pressures nor any love lost for politics, but instead to be there as his youngest son starts school in just over a week.

"No, I love it [politics].

"It is a bittersweet day. I could stay for a long time but I wouldn't get to know my kids as much as I should."

Kiritapu Allan would take over as Justice Minister, Michael Wood Immigration and Willie Jackson Broadcasting.

Ardern said Mallard had also previously indicated his desire to step down this term. He would take up a to-be-announced posting in Europe.

Mallard had been an MP over 30 years, and run into many a controversy in that time, including as Speaker. Last year he falsely accused a former parliamentary worker of rape, costing the taxpayer $330,000 in legal fees, and more recently faced criticism over his handling of the protests outside Parliament.

Ardern said his role as Speaker was a "difficult one" but she also pointed to positive achievements including making Parliament more family-friendly.

Ardern said deputy Speaker Adrian Rurawhe would be nominated to replace Mallard.

Te Pāti Māori co-leader Debbie Ngarewa-Packer said they welcomed the promotions of several Māori MPs.

"In Trevor's absence Adrian brought a different dignity and synergy into the House. He has everyone's respect and that is so important," Ngarewa-Packer said.

"Willie has a long history in Māori broadcasting and he knows intimately what the sector needs.

"Adrian will be the first Māori Speaker since Tapsell, and Kiri Allan will become the first ever Māori Minister of Justice."

Former Labour Party president Mike Williams told Newstalk ZB it was clear Mallard had wanted to move on.

On Williams he said it was originally a "strange choice" for police minister.

"She has a soft, warm personality which i don't think is appropriate for police.

"When things are quiet maybe that works. Chris Hipkins is a very clever choice."

He said he didn't expect to see any major changes in approach.

On Faafoi, Mike Williams said his heart was "clearly not in it".

Priyanca Radhakrishnan would move into Cabinet retaining current portfolios including heading the new Ministry for Ethnic Communities.

Kieran McAnulty would become a Minister outside of Cabinet and Duncan Webb replace him as Labour's Chief Whip.

Dan Rosewarne and Soraya Peke-Mason would replace the two departing MPs from the Labour list.