Survivors have described the scene as the ferry came to a halt, tipped on its side and quickly began sinking.
"There was a really loud noise and then the boat immediately began to shift to one side," rescued passenger, Kim Song-muk told the BBC.
"People were scrambling to get to the upper decks, but it was difficult with the deck slanted over."
Another survivor said: "There was an announcement telling us to sit still, but the ferry was already sinking."
"I heard a big thumping sound and the boat suddenly started to tilt," a rescued student told CNN affiliate the YTN news channel by telephone.
"Some of my friends fell over and started bleeding. We jumped into the water and got picked up by the rescue boats," he said.
Another student, Lim Hyung-min, told how he jumped into the ocean wearing a life jacket with other youngsters and then swam to a nearby rescue boat.
"As the ferry was shaking and tilting, we all tripped and bumped into each another," Lim said.
Another survivor told YTN he was "certain" many people were trapped inside the ship as water quickly filled up inside and the severe tilt of the ferry kept them from reaching the exits.
"The announcement told us that we should stay still, but the ship was already sinking and there were a lot of students who did not get out," he said.
"It was very tense," another survivor said." The ship was tilted more than 45 degrees."
"Don't move," a voice warned, according to a recording obtained by YTN. "If you move, it's dangerous. Don't move."
"Kids were forced to stay put," one survivor told YTN, "so only some of those who moved survived."
"We were told to stay where you are, so we kept staying," survivor Hyun Hung-chang told YTN.
"But later on, the water level came up. So we were beside ourselves. Kids were screaming out of terror, shouting for help."
Some of those who jumped or made their way to the top of the ship were rescued. Helicopter crews plucked some from the deck.
"I had to swim a bit to get to the boat to be rescued," Lim Hyung-min, one of more than 300 Seoul high school students who was aboard the ship for a four-day field trip, told YTN.
Survivor Koo Bon-hee, 36, told Sky News that many people were trapped inside the vessel by windows that were too hard to break.
Grieving family members, who had gathered on the quay of Jindo Island, huddled in blankets against the cold as they waited for any news on Thursday.
"If I could teach myself to dive, I would jump in the water and try to find my daughter," Park Yung-suk told Reuters.
As coastguard officials arrived for the second day of searching relatives jeered them, shouting: "The weather's nice, why aren't you starting the rescue."
Sources: BBC, CNN, Sky News, Reuters
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