At least three people are reported to have died and many more are injured after the Costa Concordia ran aground in Italy.
The cruise ship, which was carrying 3,200 people, began sinking last night near the island of Giglio, off the Tuscan coast.
Twenty four British passengers are believed to have been on board, said the UK Foreign Office, which is sending a team to the scene. The Foreign Office said it was not aware of any British fatalities.
At least 50 people are believed to be unaccounted for, although Italian officials have stressed that the passenger list may not be completely up to date.
Rescue teams are now going from cabin to cabin, searching for survivors.
The Costa Concordia had left the port of Savona at 7pm local time and was sailing to Civitavecchia, its first port of call, when it ran aground at around 9pm.
Reports said passengers were eating dinner when they heard a long bang, and were told the ship was suffering electrical problems.
The 290-metre (950 ft) vessel ran aground, starting taking in water and listed by 20 degrees, the local coast guard said.
Orders were given to abandon ship, Deodato Ordona, a cabin steward on the Costa Concordia, told the BBC.
“We announced a general emergency and took passengers to muster stations,” he said.
The £450m Costa Concordia is one of the biggest ships in the Costa fleet. It has 1,500 cabins and was at the start of a seven-day cruise of the Mediterranean.
Costa Cruises said in a statement: “Our first thoughts go to the victims and we would like to express our condolences and our closeness to their families and friends.
“In this moment all our efforts are focused on the completion of the last emergency operations, besides providing assistance to the guests and the crew who were onboard.”
It added: “The company will fully co-operate with the relevant authorities in order to determine the causes of what happened.”
Micky Arison, chief executive of Costa owner Carnival Corporation, used Twitter to send a personal message, saying: “Tonight our thoughts and prayers are with the passengers and crew of the Costa Concordia.”
The Passenger Shipping Association issued a statement insisting that the grounding of Costa Concordia was an isolated incident, as the industry sought to reassure potential passengers over the industry’s safety record during the peak ‘wave’ booking period.
The Foreign & Commonwealth Office has issued details of phone numbers those concerned about Costa Concordia passengers should contact: +39 06 4220 0001 (Italy) or 0207 008 1500 (UK).