The future of the Labour's president appears to be in doubt after Prime Minister Jacinda Ardern refused to express confidence in him over his handling of sexual assault accusations against a party staffer.

And she's also raised the possibility she may have been misled.

Ardern repeatedly told reporters she was deeply concerned, incredibly frustrated and looking for answers on Monday as she faced questions about reports of an alleged sexual attack on a 19-year-old Labour volunteer by one of the party's staff.

The party this year investigated seven formal complaints about the male staffer - employed by the Parliamentary Service - but concluded no disciplinary action was warranted in July.

The complainants later went to media with concerns they weren't being taken seriously and the party last month said it was launching a review of its investigation.

The Spinoff website on Monday published a detailed account of an alleged sexual assault by the staffer against one of the complainants, graphically describing how he had pinned her to the ground and attacked her at his home in February 2018.

Ardern on Monday told media she had previously sought assurances and been told none of the allegations were of a sexual nature - a sentiment that had also been conveyed to media - and that she wanted an explanation about the conflicting reports.

"I want to make it very clear that I am deeply concerned and incredibly frustrated by the process that has been undertaken by the Labour Party, but also by the nature of the allegations," she said.

"I was informed, in the very beginning, that the allegations made were not sexual in nature. That is obviously directly counter to what is now being reported."

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Ardern said Labour's NZ Council – the top body which ran the original investigation – was not the appropriate place to "ever" conduct an inquiry into sexual assault.

Asked if she had been misled by party president Nigel Haworth, who has been handling the allegations, or the party, Ardern said she expected the new review to get to the bottom of the matter.

"I have had differing accounts relayed to me. I do need a third party - someone who is a trusted, reliable individual - to give me a sense of clarity," she said.

Questioned if she still had confidence in Haworth, Ardern replied: "I think it's fair to say that the president has, of course, articulated to me that he only wants to ensure he has done the right thing throughout this process. But I need complete clarity."

"I have not received it through the competing reports to date."

The Herald has requested comment from Haworth.

In a statement to the Spinoff, he said no part of the original investigation had looked into sexual assaults.

"The person leading the original review made it clear to the complainants that the party would never be the appropriate body to handle allegations of that nature and that they would need to be investigated by the police," he said.

The complainant told the website she did not want to raise the issue with police because she had seen others struggle through the process, but had explicitly discussed the alleged attack during a hearing with the Labour panel hearing complaints in March this year.

The staffer at the centre of the allegations had not been in the parliamentary precinct since the review was launched and would not return at least until it was complete, Ardern told reporters on Monday.

That came after calls from the National Party's Paula Bennett for him to be stood down during the duration of the review.

The lawyer for the staffer has declined to reply to a request to comment today.

In a statement, Parliament Speaker Trevor Mallard said no complaint had been made to Parliamentary Service - the man's employer - by anyone involved in the case, either.

"I repeat my request for any individual who feels unsafe at work or when visiting to contact me or the general manager. Any further action requires a complaint," he said.