Carnival Australia admits they wrongly accused a passenger of sexual assault before he was bashed up by the apparent victim's father

The incident with Sydney man John Sun occurred after security onboard the Carnival Australia cruise were told a man had exposed and touched himself in front of young passengers. Photo / Supplied

Carnival Australia has admitted a Sydney passenger was wrongly accused of sexually assaulting children and possibly himself attacked by one victim's father before he pointed out the mistake.

Sydney father John Sun is taking legal action against Carnival Australia after the alleged incident on an eight-day return cruise from Sydney to New Caledonia in December 2016.

His statement of claim lodged with the NSW District Court suggests onboard security was told a man had exposed and then touched himself in front of young female passengers.

In its defence lodged with the court, Carnival says two of three victims identified Sun as the offender after being shown his photo.

The cruise company argues the father of one of the victims was then able to find Sun in his cabin because they were staying in a neighbouring room.

Carnival says it doesn't know if Sun was attacked as he claims so it can't admit that allegation.

But it acknowledges if the Sydney dad was subsequently detained by the ship's security officers it was because "the plantiff (Sun) had been assaulted by the father of a complainant and (it was) for his own safety and the good order of the ship".

Sun alleges security marched him to a room where they grilled him for one and a half hours and he felt he "was not at liberty to refuse the direction to accompany them".

Carnival's version of events states Sun "was asked to and agreed to accompany the security officers to the security office to assist them with their inquiries".

Court documents say that if he was detained "it was necessary, reasonable and justified".

The company says while it would have preferred a quieter approach "that opportunity was precluded by the actions of the assailant".

Carnival's defence admits Sun later "pointed out obvious physical differences between himself and the person depicted in the CCTV footage, namely that the plaintiff's legs and arms were tattooed whereas those of the person appearing in the CCTV footage were not".

Sun claims he was denied medical treatment, however, Carnival says a nurse was sent to his room.

He's suing Carnival PLC for breach of contract, misleading or deceptive conduct, defamation, unjustified or unlawful detention and negligence. He is seeking more than $100,000 in damages.

The case is due back in court on May 3.