A baby girl for NZ PM Jacinda Ardern

Boris Jancic
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NEW ZEALAND JACINDA ARDERN BABY GIRL

NZ PM Jacinda Ardern and partner Clarke Gayford have welcomed their first child, a girl

New Zealand Prime Minister Jacinda Ardern has given birth to a healthy baby girl, sparking jubilation at home and headlines around the world.

"Welcome to our village wee one," the 37-year-old politician posted on social media on Thursday, alongside a picture of the newborn.

The baby - her and partner Clarke Gayford's first - was born at 4.45pm (local time) weighing 3.31kg (7.3lb).

Both mother and daughter were doing well, the prime minister's office announced in the evening, ending days of nationwide baby-waiting.

"I'm sure we're going through all of the emotions new parents go through, but at the same time feeling so grateful for all the kindness and best wishes from so many people," she said in a statement.

There was no mention of a name, although Ms Ardern earlier warned the couple were struggling to pick one.

She had arrived at New Zealand's largest public hospital early in the morning, driven by Mr Gayford.

Still texting staff after going into labour, she only handed over the reins of power to her deputy after getting there.

Ms Ardern becomes the first elected world leader to take maternity leave - and only the second to have a child while in office. She is expected to take six weeks off.

The announcement of the birth spurred celebrations and an outpouring of congratulations on social media and across the globe.

At home, former NZ prime minister and senior UN official Helen Clark described it as "inspirational", while NZ Opposition Leader Simon Bridges, said he was delighted for the new parents.

Meanwhile, major media organisations in the United States, Britain, Australia, Europe and Asia launched breaking news banners with the announcement.

Australian Prime Minister Malcolm Turnbull told the ABC he was "really thrilled", while Britain's Theresa May, and the United States' ambassador to New Zealand also sent their congratulations.

For her part, Ms Ardern has played down the global attention she's received as a role model in recent months.

"I am able to do what I'm doing because I have enormous support around me and it makes me quite privileged," she said in a recent interview.

Born on June 21, her baby will share a birthday with Pakistani prime minister Benazir Bhutto, the only other elected leader to have a child while in power. It's also Prince William's birthday.

The pregnancy news late last year came as a surprise to the reluctant Labour Party leader, who had to simultaneously deal with intense negotiations to form a government and morning sickness.

She has since faced a stream of personal questions, parenting advice and media attention.

And recently she has also had to talk down her coming absence from politics, assuring NZ it'll be business as usual during the time off.

While her day-to-do duties will now be handled by the enigmatic Deputy Prime Minister Winston Peters, 73, Ms Ardern will be on call for any major decisions.

Mr Gayford, a 40-year-old television presenter, will be the child's primary carer after the prime minister returns to parliament.