Hundreds of passengers remain missing several hours after a South Koren passenger ferry sank with 475 on board, 100 km south of the Korean peninsula.
About 180 passengers, including high school students, were plucked to safety in Wednesday's dramatic rescue, although at least two people had died.
Al Jazeera's Harry Fawcett, reporting from Seoul, said that at least 290 passengers are still missing, hours after the ferry sank. The two passengers who are reported dead are a crew member and a teenaged student, Fawcett reported.
The ferry, identified as the Sewol, was carrying 475 passengers and crew and 150 vehicles, according to Korean port authorities, when it began to list badly as it neared Jeju island.
Within hours, television pictures showed the Sewol lying on its port side. Soon after the ship had completely capsized, with only the forward part of its white and blue hull showing above the water.
The students and teachers were on a field trip to Jeju when the ship sank.
A distress signal was sent from the ship early on Wednesday, the South Korean coastguard said, triggering a rescue operation involving dozens of ships and helicopters.
The US Navy's Seventh Fleet also has sent a ship with helicopters on board to join the search-and-rescue operation.
There was no immediate indication of what caused the ship to list and roll on its side, although one witness told YTN television there had been a "loud impact and noise" before it started sinking.
The coastguard later said one person had been found dead inside the sinking ferry. An official from the Mokpo Hankook hospital on the mainland said another person had died soon after arriving at its emergency ward.
Television and still pictures showed the badly listing ferry surrounded by debris, rescue ships, helicopters and at least one inflatable lifeboat.
Fawcett reported that at least six people were reported injured – some with bruises and others with burns.
"This suggests something pretty violent may have happened on that ship so we can probably expect the number of injuries to go up," he said.
The ferry had left from the port of Incheon, about 30km west of the capital, Seoul, late on Sunday.
A passenger on board told YTN television the first rescue helicopter had reached the vessel soon after the distress signal was sent.
The unidentified passenger, who spoke before people were evacuated, sounded calm and said those on board were in their cabins but were having trouble keeping their balance.
Heavy fog had set in overnight off the west coast, leading to the cancellation of many island passenger ferry services.