Prime Minister Jacinda Ardern says the Labour Party has "absolutely" learned the lessons from last year's infamous Young Labour summer camp, and the current allegations of sexual harassment will be a test of that.

At least four members of the Labour Party have reportedly resigned over an investigation into allegations against a parliamentary staffer who works for the Labour Party.

Newstalk ZB political editor Barry Soper said that there were 12 alleged complainants and the allegations involved not only sexual assault, but also rape and offers to pay for sex.

The Herald understands that no disciplinary action was taken following a Labour Party internal investigation, but Ardern confirmed that an independent review of how the investigation was conducted was under way following further complaints.

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"We need to be open to the fact that we don't always get it right ... We do need to learn from the mistakes of the past. We do need to change the way we do things," she told reporters on her way to Labour's caucus meeting this morning.

She would not comment on the case because the review was not yet complete, and would not say whether the alleged offender was still working for the party.

She was not aware of any complaints made to the police or to Parliamentary Service, which employs parliamentary workers, adding that it would be appropriate for people with complaints "of that nature" to take them to the police.

Speaker Trevor Mallard, who is responsible for the Parliamentary Service, said complainants should take any allegations to the police or to the employer.

"Neither I nor the Parliamentary Service have received any complaint against anyone currently working for the Parliamentary Service."

Asked if there was a culture problem in the Labour Party, Ardern said: "I can't ignore the fact that a complaint has been made. Does this mean, that as a whole, this is the experience of every Labour Party member? No. Nor do I want to be dismissive of what the complainants are raising. We need to take that seriously."

Allegations of sexual harassment rocked the party following a Young Labour summer camp in February last year.

A 20-year-old man was charged with four counts of indecent assault at the Waihi camp.

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It led to an independent review of the party's processes, and while that review has not been released due to the ongoing legal action, its recommendations were made public.

These included developing policies on sexual harassment, sexual assault, alcohol, events, host responsibility and bullying.

Ardern said that the party had "absolutely" learned from the incident at Waihi, and the current review was a chance to see what, if anything, the party should do differently.

"This has been a test of whether or not we've now learnt from that, and the party's taking a good look as to whether or not we're satisfied with the natural process of justice and whether or not we've supported the complainants as we should have."

Party president Nigel Haworth refused to answer questions on his way to the Labour caucus meeting this morning.

Finance Minister Grant Robertson said it was a matter for the party.

"The Labour Party is dealing with issues you're well aware of going back to the summer school.

"I always want everybody to feel safe in the Labour Party ... the party needs to make sure it does everything it can to make that happen."

National Party leader Simon Bridges said he did not know the details of the case.

"It seems to me we have very serious allegations and they are matters, ultimately, for the Labour leader Jacinda Ardern."