A second person has come forward saying Labour president Nigel Haworth and the party's investigating panel were made aware of sexual assault claims about a Labour staffer.

The man's comments, made on Radio NZ this evening, lend support to a 19-year-old woman's claims that she told Haworth and the panel, via email as well as verbally, about an alleged sexual assault by the staffer at a private residence.

He also told RNZ that the staffer had shoved him against a wall and, on a separate occasion, tried to punch him after being confronted about his alleged misconduct.

Lawyers for the staffer say the claims are "without foundation". The investigating panel, which looked into seven formal complaints earlier this year about the staffer's behaviour, found no disciplinary action was needed.

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Since then there have been further complaints and Maria Dew QC has been brought in to review the process and, at Prime Minister Jacinda Ardern's request, the substance of the complaints.

The claims have left Ardern "deeply concerned and incredibly frustrated" because she was repeatedly told by the Labour Party that the complaints were not of a sexual nature.

Haworth has doubled down, saying that neither he nor the panel were told about the sexual assault allegation.

But the man said that is wrong as he raised claims of sexual assault with the panel.

"I told them about his experiences with other women that were tantamount to sexual assault ... but of course being aware that they weren't my stories and they would have to talk to those individuals themselves as part of that investigation process," he told Radio NZ.

He said that he also personally raised it with Haworth.