A dream Christmas cruise has turned into the holiday from hell, according to passengers who claim as many as 400 travellers have been struck down with the norovirus winter vomiting bug.

One traveller aboard the P&O liner Oriana, which is on a 10-night Baltic cruise out of Southampton visiting Christmas markets, said people felt like they were sailing on a "plague ship".

P&O's parent company Carnival said there had been "an incidence of a mild gastrointestinal illness" among the passengers.

The spokeswoman added that, as of Thursday, out of 1,843 passengers "the number of passengers with active symptoms is six".

One passenger, Paul Gilman, 62, told the Daily Mail: "It has been outrageous from start to finish. People were falling like flies, yet the crew were trying to insist everything was fine.

"Everyone is saying this is a plague ship. It's a living nightmare."

Another passenger, Brian Weston, 67, from the Isle of Wight, said: "It's been a shambles from start to finish. Passengers became ill almost immediately we set sail and the outbreak swept like wildfire through the ship.

"At one stage there were dozens and dozens of people falling ill, though the ship's senior officers were trying to play it down."

His wife, Denise, 60, said: "A viral specialist who is a passenger told us the ship should not have set sail for 48 hours and should have gone through a deep clean."

The UK's Health Protection Agency has reported a 72% increase in the vomiting bug so far this season.

The Oriana left Southampton on 4 December, with passengers paying up to £1,400 for the voyage, which included visits to Copenhagen, Oslo and Amsterdam.

The Carnival spokeswoman said: "Enhanced sanitation protocols have already been implemented to help minimise transmission to other passengers. These comprehensive disinfection protocols have been developed by P&O Cruises in conjunction with UK and US public health authorities.

"The safety and comfort of passengers and crew is always our number one priority.

"As is currently standard procedure across our fleet, all the ship's passengers were provided with a precautionary health notice advising of widespread norovirus activity and the health measures to avoid contraction and spread, both on board and while ashore."