Ships and helicopters are taking part in a major rescue operation after an Italian ferry carrying 478 people caught fire north-west of Corfu.
One person has died after jumping from the ship and another has been confirmed injured, officials say.
A total of 190 people have been rescued but more than 280 remain on the Norman Atlantic which was travelling from Patras in Greece to Ancona in Italy.
Choppy seas and strong winds are hampering the night-time rescue.
Most of those on board were Greek. Others came from Italy, Turkey, Albania, Germany and many other countries, officials said.
A passenger manifest said that two Britons were on board, but the BBC understands that there may have been as many as six.
Italian media say the fire broke out on the ferry's car deck before spreading.
Rescued passengers include a seven-month pregnant woman and her two children, who are all being treated for hypothermia, according to Italian media reports.
Two Italian and two Greek helicopters are taking turns to winch passengers from the ship, two at a time, Greek officials say.
"This is a complicated rescue mission... The visibility is poor and the weather conditions are difficult, but we are confident because there are a good number of ships in the area," Greece Merchant Marine Minister Miltiadis Varvitsiotis said.
Mr Varvitsiotis later told reporters the fire had been brought partly under control.
"It will be a very difficult night, a night in which we hope we will be able to rescue all on board," he said.
Nearby merchant vessels aligned themselves in formation to protect the ship from waves and facilitate the rescue.
Italian and Albanian teams are also taking part in the rescue operation - some 19 nautical miles from the Albanian coast.
One of the passengers told Greek TV station Mega: "On the lower deck, where the lifeboats are, our shoes were starting to melt from the heat."
Another passenger told the same station that smoke was engulfing the ship.
"We are outside, we are very cold, the ship is full of smoke, the boat is still burning, the floors are boiling, underneath the cabins it must be burning since 5 o'clock, the boats that came (to rescue us) are gone, and we are here. They cannot take us," they said.
The wife of one of the cooks told journalists she had had a call from her husband saying: "I cannot breathe, we are all going to burn like rats - God save us."
Another passenger said some of those on board were suffering from hypothermia, including young children.
"It's pitch black. It's freezing", they told a friend by telephone.
It is not yet clear what may have caused the fire.
The chief executive of the Visentini group that owns the vessel, Carlo Visentini, said the ferry had passed a recent technical inspection despite a "slight malfunction" in one of the fire doors, Italy's Ansa news agency reports.
"The tests confirmed that the boat was in full working order," he said, adding that the fire door had been repaired "to the satisfaction of the inspectors".
Ferries are an important mode of transport between Greece's hundreds of islands as well as neighbouring countries.