Prime Minister Jacinda Ardern's baby daughter could end up voting for National, according to leader of the opposition Simon Bridges.

Bridges was on Radio Hauraki's breakfast show this morning and was asked by the hosts whether he "hated" the baby.

"Look, I don't think it's going to do a lot to help my poll ratings, let's put it that way, but you know I don't hate it! Hate is a strong word, I should say, I wish her all the best," he said.

Ardern gave birth to a baby daughter late yesterday afternoon.

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Bridges was then asked if it seemed politically correct to have a female baby, to which he responded "only under a Labour government".

Hosts Matt Heath and Jeremy Wells asked if the baby should be considered gender fluid at this point.

"She should be going to school like in boy's clothes right?" asked Bridges.

The hosts then checked if Bridges thought the baby had already cost the taxpayer much money - she was born in a public hospital. Bridges agreed.

Some baby crying sounds were then played, while the two hosts and Bridges tried to guess whether the baby was saying "capital gains tax" or "governing by committee".

Bridges was asked how he would make sure the baby voted for National when it turned 18.

"Here's the deal. See her parents I reckon were solid blue, I mean he's a cop right, cops vote blue. They know we're strong on law and order," Bridges said.

"Jacinda went to uni. She got some funny ideas. But that baby is going to be spend a lot of time with her grandparents."

Near the end of the interview Bridges turned serious for a moment saying, "in all seriousness", he wished the baby and Ardern well, and said the baby looked "amazing".

But he didn't think Ardern would ever hear his message.

"You know why I'm saying these things right now? Because I know that nothing I say is going to make the news in the next like seven days," Bridges told the Hauraki hosts.

"I'm in a complete news vacuum."