Jacinda Ardern welcomes baby girl

Jacinda Ardern's Instagram post announcing the birth of her child. Photo: Jacinda Ardern/Instagram.

Prime Minister Jacinda Ardern has given birth to a baby girl.

In a statement, Ardern's office confirmed she gave birth to a "healthy baby girl", weighing 3.31 kilograms, at 4.45pm on Thursday.

"I'm sure we're going through all 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. Thank you," Ardern said.

The Prime Minister shared a photo of her and partner Clarke Gayford with their new arrival on Instagram, saying: "Welcome to our village we one."

Political parties have been quick to acknowledge the news, with National leader Simon Bridges congratulating Ardern.

“Being parents is a joy and a privilege and we are sure your new arrival will fill your lives with all the happiness our children have ours.

“Congratulations to you both. Our family wishes yours every happiness.”

Green Party co-leader Marama Davidson congraulted Ardern on behalf of the party, saying: "As a mum, my heart is bursting with pride and love for the Prime Minister and her whanau, and [we] wish them the very best for their future."

Early on Thursday morning, Ardern's office announced she and Gayford had headed to Auckland City Hospital to have her baby and that Winston Peters was now Acting Prime Minister.

"The Prime Minister’s Office can confirm that Jacinda Ardern has arrived at Auckland hospital, with her partner Clarke Gayford, to have her baby," the office said in an emailed news release.

"Deputy Prime Minister Winston Peters is now Acting Prime Minister," the office said.

"There will be no further formal announcements from the Prime Minister’s office till Jacinda Ardern and Clarke Gayford announce the birth of their baby."