A man and a woman arrested on suspicion of assault after a mass brawl on a cruise ship have been released from police custody but remain under investigation.

Witnesses said the fight erupted in the buffet area onboard P&O’s Britannia in the early hours of Friday morning after a day of “patriotic partying” while the ship was en route to Southampton from Bergen, Norway, with passengers using furniture and plates as weapons.

The ITV journalist Richard Gaisford tweeted that a witness told staff the violent confrontation ensued after one person became upset that a fellow passenger was wearing a clown outfit because they had specifically booked a cruise with no fancy dress.

The Press Association reported that an entertainer working on Britannia said a clown had gatecrashed a black-tie party held in the 16th-floor restaurant, prompting anger.

However, on Sunday P&O Cruises said there was no clown onboard.

“Following an incident on board Britannia on Thursday evening we can confirm that all guests disembarked yesterday and the matter is now in the hands of the local police,” a spokesman said, adding that P&O did not tolerate disruptive behaviour.

Hampshire police confirmed that they were not aware of a clown being involved in the brawl. A spokeswoman said: “There is no information to suggest that a clown or anyone wearing fancy dress was involved in this incident.”

Officers are still investigating reports concerning the public order incident and have appealed for information, after the arrested pair, a man, 43, and a woman, 41, both from Chigwell, Essex, were released on Sunday.

Police said three men and three women were assaulted in the melee, and that a number of injuries were suffered including significant bruising and cuts.

Gaisford, from the news programme Good Morning Britain, said he became aware of the incident at 2am when security were called over the emergency PA system to urgently attend the 16th-floor restaurant.

He tweeted that he had been told “there was blood everywhere”, with witnesses saying they were “so frightened they had to hide” as passengers “used furniture and plates as weapons” after a day of heavy alcohol consumption by many guests.

“One witness, part of a group involved in the trouble, explained to staff that things kicked off when another passenger appeared dressed as a clown,” he wrote. “This upset one of their party because they’d specifically booked a cruise with no fancy dress. It led to a violent confrontation.”

He added: “The buffet area was immediately sealed off as medical teams went to help the injured. Staff told me they’d never experienced anything like it and those behind the violence were confined to a cabin for the last day of the cruise, waiting for police here in Southampton.”