Plates and furniture were reportedly used as weapons in a mass brawl on a cruise between Norway and England sparked by a clown.
British police are investigating the fight on the P&O vessel Britannia, with two arrests made when it docked in Southampton.
Reports suggest the incident was fuelled by large amounts of alcohol. Passengers attending a booze-fuelled 'patriotic' black-tie event on Friday were upset when a man dressed as a clown showed up.
Within minutes there was "blood everywhere", a journalist on board tweeted.
"Passengers used furniture and plates as weapons," said ITV's Richard Gaisford. Witnesses told me they were so frightened they had to hide, as family groups fought.
"The violence occurred on the final leg of a week long cruise to Norway's fjords. I became aware of trouble when officers made an emergency tannoy at 2AM for security staff to rush to the 16th floor restaurant. I went too and found passengers shocked by what they'd seen.
"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. This upset one of their party because they'd specifically booked a cruise with no fancy dress. It led to a violent confrontation."
He said staff had "never experienced anything like it".
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Nine people suffered injuries, the Daily Mail reported. The violence happened 12 hours after it left Bergen.
"Following an incident on board Britannia on Thursday evening we can confirm that all guests have now disembarked and the matter is now in the hands of the local police," P&O said in a statement.
One expert said brawls are becoming increasingly common on ships thanks to cruising's growing popularity, the sheer amount of alcohol on board and a lack of security.
"The cruise line typically claim that their security guards are 'highly trained', but all too often the security personnel and ship officers are filmed kicking and beating passengers (or they are preoccupied with trying to stop passengers from filming the out of control violence)," Jim Walker wrote on Cruise Law News, adding that prices have come down in recent years making cruises more accessible.
"The 'wider audience' will undoubtedly include a younger crowd from a different demographic, including what I call the hard partying 'Bud Light-tank top' crowd."
The Britannia was launched in 2015 in a ceremony attended by Queen Elizabeth II.