Four young Labour Party supporters were allegedly sexually assaulted at a "Summer School" camp last month.

Two males and two females, all 16, were allegedly assaulted or harassed by a 20-year-old man during a party at the Waihi camp, Newsroom has reported.

Newsroom said the man was reportedly intoxicated and put his hand down the pants of at least three of the four young people.

According to the Young Labour website, Summer School is an annual event attended by young activists, people from across the party and other leaders in the wider community for a collaborative weekend of policy discussion, campaign preparation and team building. This year's camp was in the Karangahake Gorge.

Labour leader and Prime Minister Jacinda Ardern was caught by surprise when asked by the Herald about the allegations of sexual misconduct and drinking, saying she had not been told about it.

"This is the first I have heard of any such allegations but now that you've made them I will happily investigate because that is not the behaviour that I would expect of any Labour function."

She said if the reports of the alleged behaviour were correct "I would be hugely worried by that".

She would have expected there to be safeguards in place and an appropriate level of supervision, given the ages of those involved. She did not know how many of those who had attended would have been under 18. "And I can't even say whether or not there was alcohol there. Certainly when I was there I didn't see any sign of it."

Ardern said she had attended the Summer Camp opening, where she spoke, and there was no such behaviour apparent when she was there.

Labour's General Secretary Andrew Kirton was seen in the Beehive earlier today, but Ardern said she had not caught up with either Kirton or the party president Nigel Haworth since returning from the Pacific.

She said she would look into the allegations personally before making any further response.

According to Newsroom, the man at the centre of the allegations was removed from the camp on the Sunday morning.

According to witnesses, a large variety of alcohol was available on Saturday night and many people, including a 15-year-old boy, were drinking, Newsroom reported.

It was understood the camp's supervisor, Tess Macintyre, had gone to bed and was not present at the party.

One of the camp's organisers had been in touch with the victims and informed them the incident had been reported to Labour's Head Office, Newsroom said.

She was understood to have apologised on behalf of Young Labour and offered to support them in any way she could.

Labour's General Secretary Andrew Kirton told Newsroom he was aware of the incident and was currently "working through it".

Haworth is expected to comment soon.