3:50pm - Jacinda Ardern's father says becoming Prime Minister "in her DNA"

Jacinda Ardern's father Ross Ardern was at Government House to watch her be sworn in as Prime Minister this morning.

"It was very emotional, a wonderful experience and I enjoyed it a great deal," Mr Ardern said.

"I always knew that she was destined for high office, it was in her character and in her makeup, she was always going to shine."

Ms Ardern's mother couldn't attend the ceremony as she's in London with the Prime Minister's sister, who gave birth today.

"It's in her DNA. She will work hard for everybody," he told Newshub.

3:30pm - "My job is just to make sure she's ok" - Clarke Gayford

"I think the big grin on my face says it all. I'm still coming to terms with it really, but enormously proud," Jacinda Ardern's partner Clarke Gayford said.

"My job is just to make sure that she's okay and to be in the background going have you eaten your lunch? Have you slept properly? You've got lipstick on your teeth. That's my job."