Hundreds of passengers have fallen ill after an outbreak of norovirus on a cruise ship which set sail from Southampton, health officials have said.

Some 252 of the 919 passengers on board Balmoral have fallen ill since it left the UK on April 16, according to the US Centres for Disease Control (CDC).

The ship's owner, UK-based firm Fred. Olsen Cruise Lines, said the majority of the holidaymakers are British.

The company issued a statement which said it is ''undertaking extensive sanitisation measures and cleaning of the ship''.

It added that Balmoral has not been quarantined in any port and is continuing the cruise ''as planned'', arriving in New Brunswick, Canada, on Monday.

Specimens collected when the ship docked in the US city of Baltimore between April 30 to May 1 tested positive for norovirus, CDC said.

Balmoral has suffered from previous outbreaks of norovirus, which can cause projectile vomiting and diarrhoea.

In relation to the latest incident, Fred. Olsen Cruise Lines said: ''It is believed that the highly-contagious gastric illness was brought onto the ship, and is spread by person-to-person or surface-to-surface contact.

''Clusters are more commonly seen in areas where people are in close confines, such as hotels, schools and hospitals, as well as cruise ships.''

Fifteen guests are currently required to remain in their cabins in a bid to stop the spread of the virus.

The ship is scheduled to return to Southampton on May 20.