The National Party has stepped up its attacks on Labour's new deputy leader Jacinda Ardern, saying she is only interested in putting her face on billboards and has achieved nothing as an MP.

The often-personal criticism during Parliament's general debate today was led by Youth Minister Nikki Kaye, whose long rivalry with Ardern was until a week ago a friendly affair.

That changed when Ardern was elected deputy leader last Tuesday, and Kaye immediately called out the Labour MP for "flip-flopping" on the pension age and letting down her fellow Gen-Xers.

During the general debate this afternoon, Kaye went further, saying the caucus reshuffle which lead to Ardern's promotion was a "superficial, cosmetic facelift".


Kaye said she "struggled to name anything Jacinda had done" in her time in Parliament - a comment which prompted howls from other MPs in the House.

After Ardern was appointed deputy, Labour leader Andrew Little said she would be the voice of a generation National had neglected. But Kaye accused her today of being absent during political debates on adoption and superannuation in the last week.

"She ... cut and run on the biggest issue facing our generation," Kaye said.

"And that is another example of what is a whole lot of photo ops, yep she'll be across every billboard, but she absolutely failed our generation on her first day in the job."

On adoption law reform, Kaye said she had worked with former Green MP Kevin Hague for a year to develop a private member's bill but Ardern had drafted "a one-line bill telling the Law Commission to write the law for her".

Kaye's criticisms were echoed by other National MPs during the debate, suggesting a strategic attack on one of Labour's biggest weapons.

Conservation Minister Maggie Barry also said Labour's caucus reshuffle was a "superficial, cosmetic makeover" and that Ardern had "achieved almost nothing".

Ardern was not in the debating chamber at the time, but said she saw the debate on television.

She said her and Kaye had made an agreement when they ran against each in Auckland Central to only talk about issues and not make personal attacks.

"I've stuck to that," Ardern said.

Kaye narrowly beat Ardern in Auckland Central in the 2011 and 2014 general elections.

Ardern shifted to the safe Labour seat of Mt Albert for the by-election last month, where she won easily.

Kaye recently returned to Parliamentary duties after taking leave to get treatment for breast cancer. She is tipped to take over as Education Minister when Hekia Parata resigns this year.