UPDATE 12.30PM: Our pregnant Prime Minister is assuring the country she and her partner have a plan ready to go.

Jacinda Ardern has announced on Facebook and Instagram that she and partner Clarke Gayford are expecting in June.

"And we thought 2017 was a big year! Clarke and I are really excited that in June our team will expand from two to three," she wrote on Instagram.

READ MORE: Ardern likely to miss out on extended parental leave

READ MORE: Twitter reacts to Jacinda Ardern's pregnancy

"I’ll be Prime Minister AND a mum, and Clarke will be “first man of fishing” and stay at home dad."

Ardern says she has made arrangements for appropriate Ministers to act in her other portfolios over the six weeks she's away from Parliament.

At the end of the six weeks she will resume all Prime Ministerial duties.

And we thought 2017 was a big year! Clarke and I are really excited that in June our team will expand from two to three, and that we’ll be joining the many parents out there who wear two hats. I’ll be Prime Minister AND a mum, and Clarke will be “first man of fishing” and stay at home dad. I think it’s fair to say that this will be a wee one that a village will raise, but we couldn’t be more excited. I know there will be lots of questions, and we’ll answer all of them (I can assure you we have a plan all ready to go!) But for now, bring on 2018.

A post shared by Jacinda Ardern (@jacindaardern) on Jan 18, 2018 at 1:44pm PST

 

Ardern said in a statement: "We're both really happy. We wanted a family but weren't sure it would happen for us, which has made this news unexpected but exciting.

"Yesterday I met with Deputy Prime Minister to share the news and to ask him to take on the role of Acting Prime Minister for a period of 6 weeks after our baby is born.

"As is the case when I am overseas, Mr Peters will act as Prime Minister, working with my office while staying in touch with me. I fully intend to be contactable and available throughout the six week period when needed."

READ MORE: How the world reacted to Ardern's pregnancy

She found out she was pregnant just six days before taking office.

It came as a surprise, as she says she and partner Clark Gayford had been told they would need help to conceive.

She said while there would be lots of questions both she and her partner had a plan all ready to go.

READ MORE: The meaning behind Ardern's three fishhooks

A baby due in June indicates she became pregnant in September - during the election campaign. Within minutes her Facebook page was flooded with messages of congratulations.

Winston Peters will be acting Prime Minister for six weeks after Jacinda Ardern's baby is born.

But Ardern is not the first leader of a state to be pregnant while in office.

Former Pakistani Prime Minister Benazir Bhutto had her second child in 1990 - becoming the first modern head of government to give birth while in office.