Crushed with kindness: Hey Jude, it's your birthday

National MP Judith Collins has celebrated her birthday on The AM Show with a cake, a candle, and song from her political opponent.

Closing their shared weekly interview on the show, Labour MP Annette King launched into 'Happy Birthday to You' as Ms Collins was presented with a birthday cupcake in the studio.

The Minister of Energy and Resources, Ethnic Communities and Revenue was happily, and visibly, surprised.  

"I'll have to make a wish and blow it out," she said.

"Yes do that - 'one day I will be Prime Minister'," Duncan Garner teased.

But Ms Collins chose instead to wish for another National election win.

"And goodbye Bill," Garner pushed a little more, referring to the recent National leadership contest.

"No, don't be like that!" Ms Collins laughed. "We get on very well."

The now-58-year-old says she'll be working all day but hopes to spend time with family later on.

"It's a privilege to be doing the job I do, Duncan, and I'm always very grateful."

She said she's enjoying her new portfolios. Ms King piped in saying: "You'd be better as Prime Minister though Judith!"

Ms Collins replied with just as much charm: "Oh sweetheart I'm always saying that about you, as leader of the Labour Party."