Prime Minister Jacinda Ardern says she won't release the terms of reference for the Labour review by Maria Dew QC.

Speaking at a press conference on Monday, Ardern acknowledged that the Labour Party had failed to deal with the complaints adequately.

"My focus now is creating an environment of best practice," she said.

However the terms of reference for her review would not be released at the request of the complainants, Ardern said.

The Prime Minister said she has taken action over the last 48 hours to address the allegations of sexual assault involving young Labour members.

"There are no excuses for the handling of the complaints by the Labour Party and I will offer none. To do so risks minimising the seriousness of the allegations that have been made.

"We have a duty of care and we failed in it."

Ardern said she held two conference calls with the Labour Party Council over the weekend to "establish a clear path forward that is focused on the needs of complainants, but also help us examine our own actions as a party".

She said while the party has continued to maintain that they didn't receive the complaints that have since been published in the media, what's more important is the severity of the allegations that "needed to be heard".

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"That didn't happen. It is now our job to right that wrong."

Ardern said QC Maria Dew has finalised the terms of reference for her investigation, but they will not be released because complainants have asked that they not be, as well as the respondent.

"That process will be a place where those who have come forward to the party can be heard and that includes all of the issues that they have raised.

"Maria Dew QC has indicated that she does not believe her process is the place to take a look at what the Labour Party did with the complaints when they were received, nor the handling of them. That is fair."

Ardern said the QC wants to be focused on hearing the substance, not whether Labour behaved appropriately, and she will focus solely on the complainants.

As for Labour's handling of the complaints, Ardern said the party's lawyers Kensington Swan had nearly completed a piece of work on whether it behaved appropriately in the handling of the complaints.

"They will now hand that report over to an independent third party reviewer who will establish a statement of facts around the party process and what complaints were received," she said.

"This will be based on documents rather than testimonial interviews to avoid complainants having to engage in multiple processes."

The Prime Minister also said an experienced victim advocate will be appointed to look at the findings and establish systems "so it does not happen again".

Minister Poto Williams, who has experience working in the sexual and family violence sector, will lead a culture change for Labour and will bring in experts, Ardern added