South Korean officials say three people are dead and at least 290 missing after a ferry sank off the country's southern coast Wednesday.
The boat was carrying more than 459 people, mostly students, to the resort island of Jeju when it sank in what appeared to be calm conditions.
Many are feared to be trapped inside the submerged ship or stranded in the surrounding waters, which were only 12 degrees Celsius.
Dozens of helicopters and ships, including a U.S. Navy amphibious assault vessel, are involved in the massive search and rescue effort.
South Korean Navy SEALs are searching the sunken vessel, but officials warn that those trapped inside may not have survived.
Survivors were taken to the nearby island of Jindo. Kim Tae-young, a student, said he acted quickly when the ship started to lean.
"I held a handrail and moved toward the right side of the ferry to ride a helicopter as water kept coming in," he said.
"Water kept coming in?"
"Yes, trash cans were floating and water came up to my neck."
Many of the passengers said they were initially told to stay in their seats and not try to escape. Yoo Ho-shil said when he felt the ferry began to list, he knew he had to act.
''No, I could see it. I felt in my bones that I had to escape when I saw water was flooding an aisle next to a cabin.``
Most of the passengers were high school students headed to Jeju island on a school outing.
The students attend a school in Ansan, near Seoul. Classes were dismissed Wednesday as anxious parents gathered, waiting for news about their children.
Park Sung-ho is a father of one of the students.
"I can't even describe how I feel now. I was super nervous. Even specially trained soldiers will have a hard time if they get stranded at sea. Then what a shock it must be to those kids? I'm sure it must have felt devastating. It's even worse for the parents."
South Korean television broadcast images of the ship, as it slowly turned perpendicular to the sea before disappearing beneath the surface.
The 146-meter-long ferry departed late Tuesday from the western port of Incheon. It sank about 20 kilometers off the island of Byungpoong.
The reason for the incident is not clear. Some passengers reported hearing a loud noise before the ferry started sinking.
Heavy fog was reported in the area on Tuesday evening, but it is not known whether this contributed to the sinking.