Ardern bids farewell as NZ prime minister

Jacinda Ardern says she's "ready to be a sister and a mum" as the New Zealand prime minister prepares to leave office.

Ms Ardern will head to government house on Wednesday morning to resign her commission, with new Labour leader Chris Hipkins to be sworn in as prime minister swiftly after.

The pair spent Tuesday together, travelling to Ratana Pa for Ms Ardern's final public event as New Zealand leader.

In leaving her ministerial duties, the outgoing PM said Kiwis would still see her around but not in public debates.

"You won't find me commentating on domestic politics. I've had my time," she said.

"I'm ready to be lots of things. I'm ready to be a backbench MP. I'm ready to be a sister and a mum."

Ms Ardern surprised Kiwis and much of her party last Thursday when she announced her resignation at Labour's year-starting retreat in Napier.

After Deputy Prime Minister Grant Robertson declined to run for the Labour leadership, the party swiftly backed in Mr Hipkins, the only nominee in a leadership ballot which closed on Saturday.

It has since emerged Ms Ardern warned close colleagues, including Mr Robertson and Mr Hipkins, around Christmas last year she was exhausted and would spend the summer considering a shock exit.

Mr Hipkins said he learnt Ms Ardern's final decision shortly before she announced it last week.

Ms Ardern will head to the back bench for three months, resigning her seat in April ahead of an October 14 election.

The 42-year-old's departure also sparked speculation she was leaving due to the weight of abuse and threats towards her office, something Ms Ardern denies.

"I would hate for anyone to view my departure as a negative commentary on New Zealand," she said.

"I've experienced such love, compassion, empathy and kindness when I've been in this job.

"That has been my predominant experience. I leave feeling gratitude for having this wonderful role."

Mr Hipkins declined to share any advice Ms Ardern offered during their van trip from Wellington together.

Ms Ardern said it was "two hours of reckons" with one cut-through message.

"You do you," she said, encouraging Mr Hipkins to walk his own path.

"It's for him to carve out his own space, be his own kind of leader ... this is now for him."

The annual mission to Ratana Pa, a town in the Whanganui region, is a unique part of the New Zealand calendar.

Politicians are invited to address leaders of the Ratana Church, a Maori branch of Christianity, during the three-day festivities each year.

The church has ties to Labour dating back to a pact with Michael Joseph Savage, the party's first prime minister.

Leaders applauded and sang praises for Ms Ardern during a powhiri, or welcoming ceremony, rich with pageantry and Maori waiata, or song.

Ms Ardern closed proceedings with a short speech of thanks.

"I leave with a greater love and affection for the people of Aotearoa New Zealand than when I started. And I didn't think that was possible," she said.