Acting Prime Minister Winston Peters has wished Jacinda Ardern all the best after the Prime Minister went into labour this morning.

"It's a happy day and on behalf of the coalition Government we wish her and Clarke all the very best," Peters said.

Peters, the Deputy Prime Minister, will act in the top job for the next six weeks while Ardern is on parental leave.

His office said his diary for today remained the same.

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Peters would be in Parliament for Question Time before meeting EU Trade Commissioner Cecilia Malmstrom, then flying to Auckland for the Kea Awards this evening.

The Green Party also sent their best wishes to the Prime Minister and her partner Clarke Gayford.

"I am thinking of Jacinda with so much excitement as she approaches giving birth for the first time," Greens co-leader Marama Davidson said.

"Her and Clarke have my best wishes for this special experience."

"This is an exciting time for Jacinda and Clarke and an historic moment for our country," co-leader James Shaw said.

"I join with Marama and our Green Party caucus colleagues in wishing them both all the best."

National MP Paula Bennett raised the happy event in the House, which is sitting today under urgency.

Bennett moved a motion without notice or debate that the House wish Ardern and Gayford well on the birth of their child.

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It lightened the mood of the House, which was knee-deep in an argument over the fuel tax bill.

"It is unique circumstances that the country finds itself in today and it is a really, really big time both for the Prime Minister and for Mr Gayford and I know certainly the whole House and the whole country is kind of sitting on the edge of its seat and I just wanted to put on record that we wish her and this baby the best of health, a speedy and hopefully really pleasant birth, as good as they can be.

"I know this is an exceptional day for them and we certainly really want to wish them both, the whole three of them, the best for today," Bennett said.

Speaker Trevor Mallard said he would spread a bit of "fairy dust" in allowing Leader of the House Chris Hipkins to speak, technically entering into debate.

Hipkins added the best wishes of the Labour Party.

"The whole House wishes her all the very best. It is world-leading for New Zealand and we are all very proud of her."

The motion was passed without objection.