Prime Minister Jacinda Ardern maintains she never knew the complaints made by a Labour Party staffer were of a sexual nature despite asking the question of the party president.

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

Ardern repeatedly told reporters yesterday 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.

Ardern was grilled by Mike Hosking on Newstalk ZB this morning in which she said the party had bought in a QC four weeks ago to help her get to the bottom of the employee's complaints

"I absolutely need to be the one to fix it and that's what I plan on doing.

"We bought in a QC about 4 weeks ago and I expect I will get some clarity and some of the competing information that I have been given today through that work."

Ardern said she hadn't spoken to the victims and when questioned why, she replied that she didn't believe they had "sought to speak with me".

"That's been one thing I would say, Mike, is that in these kinds of issues when I've been advised for instance that there was a concern around how many people within the party may have known about the complaints that were being made ... which I originally was advised were not sexual in nature.

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"If they did I would happily talk to them."

When asked whether she had a duty of care to reach out to them, Ardern said the first question she asked was whether the complaints were of a sexual or physical nature.

She was told they were not.

"I was given on a no surprises basis that information via a staff member they went back and conferred with the party and confirmed that they were not.

"On that day that I was asked, i asked the question immediately and was advised immediately that it was not.

"The party themselves, of course, have continued to maintain the complaints they were now looking into were not sexual in nature. So obviously I have two pieces of very competing information.

"It's very distressing, very frustrating. I am now trying to get to the bottom of that."

Ardern reminded Hosking that she was the employer and had to be careful.

When asked why it had taken so long - with the complaint being laid in February and it was still going.

"The complaint as I understand was made about 6 months ago, the investigation by the party started then. They concluded. Those involved were dissatisfied with the process and complaints were made about that and that's when a third party was bought in.

"And now since then we've had statements made that directly contradict the very nature of the complaints.

"Now I need to get clarity so I can act on it."

When asked if she could sack the president, Ardern said if a report found that the party hadn't dealt with the matter appropriately "or that there's been failures on his part, he would do what's in the best interests in the party and those involved".