Prime Minister Jacinda Ardern said she asked senior leadership about a sexual assault claim when media reports about the complaints first surfaced five weeks ago, but would not say if she asked recently-resigned party president Nigel Haworth.

She said the process had caused harm. "There is no doubt of that. That is why I have given an apology to those involved."

She would not say whether she had spoken to the three party investigators that had decided in July that no disciplinary action was needed against the Labour staffer at the centre of accusations.

She would not be drawn on whether Grant Robertson had talked to her about sexual assault claims. Robertson has also refused to say when he was told about sexual assault claims.

Complainants have claimed that Robertson was told about the claims on June 30.

Ardern would not say whether anyone else's job was on the line, saying she would wait for the review from Maria Dew, QC.

She said the terms of reference for Dew's review were being finalised with input from complainants, and they needed to be wide enough to allow Dew to cover what needs to be covered to the satisfaction of the complainants.

"Failures have existed here and I don't need the QC process to tell me that."

She said as leader of the Labour Party, she had to fix the problem and apologise to the complainants.

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Ardern said she was not hiding behind the QC's report, and she needed to front media questions while also respecting the privacy of complainants and the QC's process.

She did not want to comment on Labour deputy leader Kelvin Davis, who reportedly referred to the allegations as "rumours" in the House yesterday.

This afternoon Davis said that his words in te reo Maori were translated as "rumours and allegations", but when asked whether that was disrespectful to the complainants, he changed his mind and said that he meant "allegations".

Tracey McLellan, who was on of the investigating panelists, was acting party president after Haworth's resignation until the ballot for a new president.

Ardern said McLellan becoming acting party president was in accordance with the party rules, but the party's NZ council could install someone else if they decided to do so.

The Labour staffer's lawyer has said the allegations are without foundation and the party's investigating panel took no disciplinary action earlier this year, but that process and the substance of the complaints are now being reviewed by Maria Dew, QC.

Yesterday Ardern read correspondence from a complainant that showed that the process had been harmful to the complainants.

She challenged party president Nigel Haworth over his handling of the complaints, who responded by resigning.

Speaking to reporters this morning, Ardern said she asked to read the correspondence, which outlined serious allegations, as soon as she knew that it existed.

She defended her response to the complaints, saying that a report in The Spinoff on Monday was the first time she had seen a sexual assault allegation from a complainant.

"Monday was the first time that I saw details that a complainant had stated that they had been sexually assaulted, and that they had taken a complaint to the Labour Party. That was the first time."

Asked why she had not acted sooner, she said that she had.

When media first started reporting a sexual assault allegation five weeks ago, she had asked the Labour Party and was told there were no such allegation, a claim disputed by the complainants.

Ardern then brought in a QC to review the matter and decided that the Labour Party needed to deal with serious complaints externally.

She also disputed claims by National Party deputy leader Paula Bennett that she must have known about the sexual assault claim months ago.

Yesterday Bennett named people close to Ardern who she said had been told about the complaints, including the sexual assault allegation.

They included Finance Minister Grant Robertson, Ardern's former chief of staff Mike Munro, Rob Salmond, who works in the Labour leader's office as well as the Prime Minister's office, Ardern's chief press secretary Andrew Campbell and Beth Houston, who works in Phil Twyford's office.

"There are so many senior people within the Prime Minister's office and other senior ministers that know and knew the extent of it that it is inconceivable that [Ardern] wasn't told," Bennett said.

"I find it very hard to believe that one of the senior people in her office didn't inform her that there was some form of sexual assault to one of her staff members. She needs to come clean with everything she has known, and when."

Asked about Bennett's comments, Ardern said: "Some of those allegations I've heard, I just absolutely refute."

She did not go into further detail.

Bennett had asked Ardern during Question Time yesterday whether she said stood by her previous statement that no senior people in her office had received a complaint.

Ardern said she stood by the statement at the time she said it.

Robertson has not said whether he was told of a sexual assault complaint in June, saying he wants to respect the complainants' privacy and the QC's work.

Bennett said that Robertson's silence was deafening, but Ardern supported his reluctance to speak out.

"I am very aware that there are vulnerable people in this situation. There is a QC process. I want to allow that to run its course and I want people to feel safe that they can engage in that process."

Ardern is awaiting the QC's report and could not say whether the Labour Party had misled her when she was told there was no sexual assault complaint.

Complainants have said that the sexual assault claim was clearly laid, both verbally and in email documents, and have released some of those documents publicly.