New Zealand leader Jacinda Ardern in hospital for birth

Jacinda Ardern in Northland June 2018

New Zealand Prime Minister Jacinda Ardern, the first pregnant world leader in almost 30 years, has been admitted to the hospital to give birth, her office said.

Not surprisingly, the PM's office won't be giving any more formal announcements until Ardern and her partner Clarke Gayford get to officially announce the birth of their child, the sex of which they haven't let slip yet.

The pregnant Prime Minister arrived at Auckland City Hospital accompanied by her partner Clarke Gayford on Thursday morning.

In a statement, her office said: "The Prime Minister's Office can confirm that Jacinda Ardern has given birth to a healthy baby girl".

Ms Ardern is set to make history as the first New Zealand Prime Minister to give birth while in the top seat.

Deputy Prime Minister Winston Peters, from the populist party New Zealand First has become acting prime minister and will run the country for the next six weeks while Ardern takes maternity leave, the statement added.

Her expected due date was June 17.

The couple announced the pregnancy to the public on 19 January.

It's Ms Ardern's first child, and her partner Clarke Gayford will be a stay-at-home father.

Further afield, Queen Elizabeth gave birth to two of her four children after ascending to the throne, Prince Andrew and Prince Edward.

The 37-year-old would become just the second elected world leader in modern times to give birth while in office, after the late Pakistan prime minister Benazir Bhutto gave birth to daughter Bakhtawar in 1990.

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