New Zealand's Prime Minister Jacinda Ardern, only the second world leader to give birth while in office, ended her maternity leave today.

Six weeks after giving birth, the prime minister announced that her baby girl, Neve, will accompany her to the United Nations next month.

The 38-year-old said she was looking forward to getting back to work and marked her first day back with a round of media interviews.

She told TVNZ: "I feel like I've been gifted by the New Zealand public, by my team and with the help of the acting prime minister this time to be with Neve, which has been wonderful.

"But of course, this is a unique circumstance and I'm really very keen to get back to work."

Ms Ardern has opted to work from home in Auckland until the weekend when she will relocate to the capital Wellington.

She said that while she and partner Clarke Gayford want to protect the baby's privacy "at the same time we want to be a family and I do a very public job".

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Mr Gayford, a television show host, plans to be a stay-at-home dad and the main caregiver for their daughter.

Ms Ardern told they would travel as a family to the UN in New York, where she is due to speak.

"Perhaps fittingly the programme for (the UN meeting) is focused on things like women, children, and climate change - very strong themes in those areas," she said.

Rather than be concerned with affairs of state while on maternity leave, Ms Ardern was "worrying about feeding, sleeping, and nappies and there's this overlay of (public) interest in what is actually something that is mundane".

"Something that every parent has gone through and yet I absolutely accept this layer of interest because it's not our normal yet. But one day it will be."

The birth capped an eventful year for Ms Ardern, who became prime minister in October just three months after taking charge of the Labour Party as it languished in the polls.

She announced her pregnancy five months before the birth.

Benazir Bhutto - the first world leader to have a child while in office - told almost no one she was pregnant until her daughter was born in January 1990.

Unlike Ms Ardern, who was able to take maternity leave, the Pakistani prime minister underwent a caesarean section and returned to work.

During Ms Ardern's absence, her deputy Winston Peters led the country.

She resumed control when he left overnight for an ASEAN foreign ministers summit in Singapore.