Image copyright Reuters Image caption Most of those on board the Balmoral are British, the cruise operator said

Hundreds of passengers on a British cruise to North America have fallen ill with norovirus, health officials say.

The US Centers for Disease Control (CDC) said 252 of 919 passengers on board the Balmoral cruise ship had had the stomach virus since leaving the UK.

Most of those on board are British, its owner, Fred Olsen Cruise Lines says.

The ship - which left Southampton in the UK on 16 April - had been subjected to "extensive sanitisation measures and cleaning", the firm added.

It docked in Portland, Maine, on Sunday, before leaving for Saint John, in the Canadian province of New Brunswick.

It has previously visited the Azores, Bermuda, as well as the US cities of New York and Boston.

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A man, who did not want to be named, told the BBC his parents were on board and had contracted the virus.

"They have been confined to their cabin for 48 hours," he said.

"My father said the ship was not allowed to dock in Hamilton and St George's in Bermuda because of the virus. They have missed out on two of the highlights of this cruise.

"They are quite fit but they're in their late 70s, which is always a worry. This was supposed to be a cruise of a lifetime for my parents but has turned into a worrying and marred escapade."

Fred Olsen said the ship had at no point in the cruise been quarantined.

Close confines

CDC experts boarded the ship while it was docked in Baltimore on 30 April and 1 May to carry out tests on people who had fallen ill, the organisation said in a statement.

Since then, the number of patients with norovirus, also known as winter vomiting bug, has increased. As well as the 252 passengers, eight of the 520 crew have also contracted the illness, the CDC said.

Fred Olsen Cruise Lines said cases were "particularly highlighted" on cruise ships, where people were in close confines. There were 15 passengers confined to their cabins, it said.

The company said it was "co-operating fully" with maritime authorities and would "continue to make every effort possible to ensure the safety and well-being of all its guests and crew".

The Balmoral has been hit by other outbreaks of norovirus in previous years.

An eight-day Scandinavian cruise on the same ship was cut short last May after a number of people fell ill with norovirus.

Image copyright Science Photo Library Image caption Norovirus is spread by human contact or surface contact

In 2010, at least 310 people on board the ship were reported to suffering diarrhoea and vomiting when it docked in Los Angeles.

And an outbreak of norovirus hit more than 100 people on the Balmoral on a cruise of Scotland in 2009.

The CDC has reported 10 outbreaks on ships docked in the US so far this year, compared to 12 for the whole of last year.

Symptoms of the illness include a sudden onset of vomiting and/or diarrhoea and some people may have a temperature, headache and stomach cramps.

The sickness, spread by human or surface contact, usually lasts one or two days.