Hipkins takes office as NZ prime minister

Chris Hipkins has been sworn in as New Zealand's 41st prime minister in a ceremony at Government House.

"It feels pretty real now," Mr Hipkins said in his first comments as PM after the official photo had been taken.

Mr Hipkins was sworn in alongside his deputy PM Carmel Sepuloni on Wednesday in Wellington, just minutes after the resignation of outgoing PM Jacinda Ardern.

Earlier on Wednesday, Ms Ardern was mobbed by hundreds of well-wishers, including her own MPs, as she left parliament on her last day in the job.

Mr Hipkins and Ms Sepuloni were congratulated by Governor General Dame Cindy Kiro, who signed their warrants of appointment.

Family and friends of the new leadership pair, including several cabinet ministers, packed Government House's ballroom for the occasion.

The ceremony completes a remarkable leadership transition from the Labour party, just 142 hours after Ms Ardern's bombshell announcement.

Ms Ardern shocked Kiwis when she announced she would be standing down as PM, citing exhaustion.

"Having reflected over summer I know I no longer have that bit extra in the tank to do the job justice. It's that simple," she said.

From that point, Labour quickly organised a leadership ballot and consulted in-house

MPs largely stayed true to a pact to keep their discussions private, with none revealing their intentions to stand ahead of the nominations deadline.

Only one MP - Ibrahim Omer - revealed a preference for leader, saying he attempted to get Finance Minister Grant Roberston to consider a tilt, calling him the "natural successor".

Mr Robertson - Ms Ardern's Deputy PM and a two-time leadership loser - decided against running, in line with a declaration he made after his last unsuccessful challenge for Labour's top job in 2014.

Internal discussions on Friday last week left Mr Hipkins as the sole leadership nominee.

He was confirmed as leader by Labour's partyroom on Sunday, when he reflected on the fast-tracked process.

"I take my hat off to the Labour MPs," he said.

"I'm so proud of our team. It has absolutely been the best leadership transition that I have ever seen in any party in the New Zealand Parliament.

"The maturity that we've seen from my colleagues and the way they've handled this process out has just been so impressive."

Mr Hipkins was in a better position than most to prepare for the transition.

He revealed on Monday that Ms Ardern gave him and Mr Robertson a headsup around Christmas that she would spend the summer considering her future.

At government house, he told Dame Cindy this was his "biggest privilege and responsibility of my life".

"I'm energised and excited by the challenges that lie ahead," he said.

Following Mr Hipkins' ascension to the Labour leadership, MPs then backed West Auckland-based MP Ms Sepuloni as his deputy.

Ms Sepuloni, raised in the Taranaki dairy farming region where her Samoan-born father worked in an abattoir, becomes New Zealand's first deputy PM of Pacific descent.

"It's very hard to fathom that a working class girl from Waitara who turned Westie can become the deputy prime minister of New Zealand," she said.

She said Mr Hipkins had honoured "me and my family and our Pacific community" with the appointment.

Mr Hipkins then hosted a cabinet meeting on Wednesday lunchtime and a post-cabinet press conference, as is traditional in New Zealand.

However, Kiwis will need to wait a bit longer to learn of new policies or Mr Hipkins' new cabinet, with the new PM batting away questions on those issues.

"I'm not going to start making announcements only a couple of hours into the job," he said.