Nearly 300 people remain missing after a ferry capsized off the southern coast of South Korea Wednesday with more than 462 people on board, most of them high school students.
Coast guard officials say 174 people have been rescued, and four are confirmed dead.
Many are feared trapped in the submerged ship or stranded in 12 degree (C) water.
South Korean Navy SEALs are continuing their search inside the sunken vessel, but officials warn those trapped inside may not have survived.
Dozens of helicopters and ships are involved in the search and rescue effort. Officials from the U.S. Navy say an amphibious assault vessel is on standby and ready provide support as requested.
The boat set off from Incheon city Tuesday night for a 14-hour trip to the resort island of Jeju when it capsized. Officials say they are not sure what caused the ship to sink, but some survivors reported hearing a loud impact before the vessel rolled to its side.
Student Kim Tae-young 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."
"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 begin 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."
Heavy fog was reported in the area on Tuesday evening, but it is not known whether it contributed to the sinking.