The trial has begun of a man charged multiple accusations of sexual assault at a Labour Party summer camp.

The now 21-year-old is charged with five counts of indecent assault against four complainants, two men and two women.

The accused, who has name suppression until at least the end of the trial, allegedly grabbed and squeezed a man's testicles, touched another man's genitals, kissed a woman on her neck and face and groped a second woman's breast and bottom.

The criminal charges followed a police investigation into the events of the Labour Party youth summer camp near Waihi on the Coromandel Peninsula in February 2018.

The accusations first surfaced publicly in March of that year against the man, whose defence team includes Emma Priest and John Munro.

Priest said her client was "a young man at a party caught up in a political storm".

He is now on trial before a jury in the Auckland District Court, which is expected to last five days.

Judge Russell Collins told the jurors the case had already generated a "significant amount of publicity" and warned them not to make any external inquiries or access any social media sites to search for more information.

In his opening address, Crown prosecutor David Johnstone said about 50 people were at the summer camp at the time, having travelled from all over New Zealand to be there.

On the night of the allegations a quiz was held, he said.

"There was music, dancing, high spirits."

But there was also excessive drinking, he added.

"It seems [the accused] more so than most had a fair bit to drink.

"It's fair to say that Mr [accused] became very drunk."

Johnstone said while inappropriate behaviour by young Kiwis at parties is "not really unusual", the accused's behaviour on that Saturday night "became not just inappropriate but also unacceptable".

"[The accused] firstly put his hand down the front of the pants of two young men," Johnstone alleged.

"To the second young man he did it twice ... This conduct was entirely out of the blue.

"Just why Mr [accused] thought it would be a good idea is not clear."

A few moments later, Johnstone told the jury, the accused allegedly "lipped his way up the neck of a young woman".

"He needed to be shoved off," he said.

Repeated attempts were then made to get the young man to bed and sleep it off, Johnstone said.

But, the prosecutor alleged, the accused made an inappropriate comment to two women helping him before groping one.

The 21-year-old couldn't remember much from the night, Johnstone said.

"Perhaps this trial is what it takes to fill in the remaining gaps for him."

Priest, however, said her client "is not a sexual offender".

"This was not criminal behaviour."

She said the first charge, an accusation of squeezing a man's genitals, was the result of the complainant wanting to be "part of the drama" created by other accusations.

The allegations relating to the second complainant, Priest said, simply didn't happen.

She said her client "did something completely different which was meant as a joke".

Priest said the accused had a complete defence to the fourth charge, an allegation of unwanted kissing.

"She wanted it," Priest said. "There is no indecent assault here."

The final allegation of groping has been described by the complainant as an "intentional fumble", the court heard.

Priest said her client doesn't recall any such incident but "is adamant he did not sexually assault her".

"There may have been some drunken antics as you might expect at a party but there is no criminal offending at all," Priest said.

Maria Austen, a Wellington lawyer, conducted an external review of Labour Party procedures after the allegations were made.

Austen's report included several recommendations, however, Prime Minister Jacinda Ardern has said the report will not be publicly released while the court proceedings were ongoing.

Ardern spoke to those at the camp the day before the allegations.