Jacinda Ardern won't say if she has confidence in Labour Party President Nigel Haworth

Prime Minister Jacinda Ardern won't say she has confidence in Labour Party president Nigel Haworth in the wake of allegations the party failed to handle sexual assault claims adequately.

Reports surfaced of the detail of allegations of sexual assault from a 19-year-old Labour Party volunteer, and her dissatisfaction with an investigation into the claims, on Monday.

The complaints were investigated in March, but no action was taken. Labour launched an investigation, led by Maria Dew QC, into how the claims were handled in August after Newshub broke the story of complainants' dissatisfaction with the party.

Ardern said she had discussed the matter with Haworth directly and implied he would resign if the investigation doesn't show him in a good light.

"I think if the findings are that he hasn't managed it properly, I think he would have his own expectation on himself," she told The AM Show.

"But he knows that I'll be dealing with it decisively once I have that report back."

On Tuesday a group calling themselves "Me Too Labour" released an open letter to Ardern calling for an apology and resignation from Haworth.

Ardern said she wasn't aware the allegations were sexual in nature and had she known she would have acted earlier.

"When I was told that there was a member of the Labour Party, that also happened to be employed in the wider team, had had complaints made about them my first question was 'what are the nature of those complaints are they sexual or physical?' The answer I was told was no.

"I then asked whether any complaints were made by other staff members, I was told no.

"Now there is very clear information contradicting that, in August we brought in a QC, that's the right thing to do, I need clarity and I will act on that because the reports and allegations I have seen are deeply distressing."

For now, she's waiting to see what Dew's investigation finds and once that comes back, she will take action.

"I absolutely believe now that this is something I need to directly step in, intervene and make right. I have a QC that is looking into the allegations that have been made, including the party's handling of those allegations.

"I want to wait until that comes back and then I will act decisively on those findings."

Newshub.