A violent brawl that broke out on a Carnival Cruise Lines ship bound for Melbourne, forcing the vessel to dock early in New South Wales, may have been sparked by a dispute over a thong.

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As many as 30 people have been injured on board what passengers have described as "the cruise from hell".

NEIL MITCHELL/3AW An image taken from mobile phone footage of the violent brawl on the Carnival Legend cruise ship.

Carnival Cruise Lines has said it called police to "remove a family group of passengers", and police officers boarded the ship on Friday morning when it reached the port of Eden on the NSW South Coast.

Scared passengers said people were bleeding and traumatised after the violent outburst on the Carnival Legend, which had been on a 10-day journey to the South Pacific.

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JAMES MORGAN The Carnival Legend cruise ship has been on a 10-day tour of the South Pacific.

On Friday, police escorted a host of passengers off the ship and into a waiting bus.

It is understood the bus will take the group to Canberra before they are flown home.

It is unclear whether any arrests have been made.

DAVID BARKHO/3AW A bleeding passenger after a brawl on the Carnival Legend cruise ship.

The Carnival Legend is scheduled to make port in Melbourne on Saturday after calling short the cruise due to the incidents.

A 21-year-old female passenger who did not want to be named told The Age on Friday afternoon she was relieved to know the situation was under control after "a rough time".

She said she believed the violence had all been instigated by one large family group of at least 20 people who "came onto the boat wanting to fight people" and were using any excuse to start trouble.

Travelling with her partner and another couple, she said their group became targeted two days ago after one member accidentally brushed past a member of the "violent" family.

"Yesterday the friend we were travelling with was subjected to a large violent outburst ... he was essentially thrown to the ground, it was completely unprovoked," she said, adding she believes the violence may have been triggered when her friend made eye contact with the group as they were chasing down another passenger.

"They had him by the neck and they were punching and kicking him," she said.

The woman and her partner spent the past two days hiding in their cabin and were looking forward to getting on with what was left of their holiday.

Another passenger identified only as Zac had told Neil Mitchell on Melbourne radio station 3AW he was going to be removed from the ship on Friday after being locked in his room by security overnight.

Zac suggested the drama between his family and another party on the ship started following a misunderstanding over a thong.

"This is all over a thong, not a foot, a thong being stepped on and being instantly apologised for. What happened there and then was apologised for," he said.

"My nephew was threatened as he was returning a soccer ... when four or five blokes walked up to him and said 'Don't worry we're gonna get ya.' "

Zac claimed security guards followed his family at "every possible moment" and aggravated the situation.

"The first hit was thrown by security towards, not just my daughter and my sister-in-law, but my wife as well," he said.

When the brawl broke out, Zac said, security guards assaulted him and his son, "taking turns pounding us in the face with knuckle dusters and steel-cap-boots".

"We're basically standing here, thanking the lord above that we survived it," he said.

Confronting footage of the brawl obtained by 3AW shows security guards were involved in the melee, although it does not show who instigated the fight.

Several guards and at least one staff member can be seen kicking a passenger while he is on the ground.

People can be heard crying and screaming in the background.

Concerned father David Barkho told 3AW his son George called him crying from the ship about 1am on Friday.

His son said "a lot of people are bleeding, a lot of people down".

"He has a head injury," he said.

"He said: 'Please, Dad, please Dad, call the federal police.

"I could hear a lot of kids crying, women screaming, swearing."

One passenger, known only as Michael, told 3AW he was kicked while lying on the ground, and received cuts and bruising to his face, back and legs.

Melbourne mother Kellie Petersen is on board with her husband and three children, aged 11, nine and six.

She told 3AW she and her husband had been threatened by the large and aggressive family group responsible for the chaos.

"Fights have been going on for a few days now," she told the radio station.

"We're scared. We've been told to watch our backs by this group so we're scared to go anywhere alone in the ship.

"We can't wait to get off."

Ms Petersen said some violent incidents had occurred in front of children in the pool.

"People are walking around with cut heads and hands, bandages everywhere," she said.

Another passenger told the Nine Network they would not leave their cabin and were scared for their safety.

Residents and onlookers in Eden said there was a large police presence at the wharf on Friday morning.

A NSW Police spokeswoman confirmed a planned police operation was under way on the ship.

"About 7am today, officers attached to Marine Area Command received reports of people fighting on board a cruise ship," the spokeswoman said.

"A number of people are expected to be removed with assistance from the operational support group."

A statement from Carnival supplied to 3AW stated: "Safety is the number one priority for Carnival Cruise Line, we take a zero tolerance approach to excessive behaviour that affects other guests and we have acted accordingly on Carnival Legend.

"The ship's highly trained security staff have taken strong action in relation to a small group of disruptive guests who have been involved in altercations on board.

"The ship's security team is applying our zero tolerance policy in the interests of the safety and comfort of other guests.

"Carnival Legend is currently on a 10-day South Pacific cruise scheduled to be completed in Melbourne tomorrow [Saturday]."

- The Age, AAP