Labour's general secretary Andrew Kirton didn't notify the Prime Minister, the police or parents that four teenagers were allegedly sexually assaulted at its summer camp last month.
Jacinda Ardern was blindsided this afternoon by allegations of sexual misconduct at the camp which she briefly attended near Waihi.
The Newsroom website is reporting that a 20 year old man allegedly harassed four 16-year-olds - two men and two women - at a boozy party on the camp's second night.
Mr Kirton said he had known about the incident for about a month and was extremely disappointed it occured.
He chose not to alert Ms Ardern, the police, or the teenagers' parents based on advice he'd received, he said.
"And the reason why we didn't, or I didn't, is because the advice that I've got is that it can add more distress when a wider group of people become aware of the incident.
"We wanted to make sure that we kept the confidentialty of those involved."
Mr Kirton said Labour had banned the alleged perpetrator from future events and has ordered an external review.
The police issued a statement this evening to RNZ saying they were aware of the media reports.
"We encourage anyone with information they wish to discuss with police, or matters they wish to report, to contact us," a spokesperson said.
Ms Ardern said she attended the opening of the summer camp and there was no evidence of any untoward behaviour while she was there and only learned of the allegations from media this afternoon.
"None of that was apparent when I was there, this is the first I've heard of any such allegations, but now that you've made them I will happily investigate because that is not the behaviour I would expect of any Labour function.
Ms Ardern said there were a range of ages at the Summer Camp and she would have expected there would have been adequate supervision.
"When I was there those who run the camp were present, but again I was only there briefly in the late afternoon and there was no sign of any of that at the point that I was present."
In a statement, Ms Ardern said she was "very disturbed" to hear the claims.
"I expect young people, and indeed anyone, attending our camps can do so knowing the environment is safe."
She said she'd sought assurances that everything was being done to support the teenagers.
"I've also asked the party to take every step possible to ensure that our events are safe for everyone who attends in the future.
"I understand this work is already underway, and started as soon as the complaints were received."
Police, PM, parents not told about sexual assault
The Labour Party has now issued a statement, saying it was extremely disappointed and deeply sorry young people at the camp were exposed to highly inappropriate behaviour.
Labour Party general secretary Andrew Kirton told Checkpoint that a decision was made not to inform the Prime Minister about the incident.
"The advice that I've got is that it can cause further distress when you inform a wider group of people who become aware of the incident, we wanted to make sure that we would keep the confidentiality of those involved and that they didn't get the impression that a whole group of other people knew who they were, knew what had happened and were talking about it."
Mr Kirton said that was the advice he was given by professional people who work in this area. The Labour Party would support any victims who wished to lay a complaint with the police about the incident, he said, although none had indicated they wished to do so.
The victim's parents were not informed and Mr Kirton said he was advised that it was up to the young people themselves to tell who they wished about the incident.
"I didn't want to go over and above their heads and cause further distress by contacting other people where they might not want to discuss it with anyone, they might want to put it behind them."
Alcohol was not supplied at the event by the Labour Party, although people were able to bring their own alcohol, Mr Kirton said.
There were non-drinking organisers at the event.
It was not appropriate to be serving large quantities of alcohol at an event which was attended by 15 and 16 year olds, he said.
Labour Party review
The Labour Party wanted to review what happened at this event, as well as ensuring that alcohol consumption did not get out of control at any future events, he said.
Labour had banned the alleged perpetrator from future events and was reviewing its policies - including those involving alcohol, the Labour Party statement said.
Young Labour had also apologised to the young people involved, Mr Kirton said.
"We are extremely disappointed that an incident like this happened at a Labour event and we are working to make sure those involved receive any support they need. We are deeply sorry for the distress that's been caused. It shouldn't have happened.
"The Labour Party has initiated an external review of our policies and procedures including those involving alcohol. This review will involve our various sector groups, including Young Labour."
The party was alerted to a situation which it wanted to ensure was never repeated, the statement said.
The complaints related to a 20-year-old man and Young Labour was alerted the morning after an evening "in which we understand several young people had consumed alcohol", he said.
"The camp organisers contacted me in the days following the event and explained what they understood had happened, and the action they'd taken in response to it.
"Those included having clear processes in place such as a dedicated welfare phone line and designated support people. We have also offered further, professional support to those involved," Mr Kirton's statement said.