Seoul, South Korea (CNN) -- Rescue boats and helicopters scrambled to pluck hundreds of passengers, most of them high school students, from a passenger ferry as it listed and slow sank off the southwest coast of South Korea on Wednesday.
Of the 474 people on board, 368 were rescued, many from the freezing waters into which they had jumped from the listing ship.
At least two people -- a woman and a student -- were confirmed dead. Another 104 remain unaccounted for, South Korean officials said.
The rescue operation was still underway at 2 p.m. local time (1 a.m. ET) -- four hours after the ferry first sent out distress signal. Authorities could not immediately say what caused the ship to sink. The weather at the time of the incident in the area was clear.
'I wanted to live' The ferry, Sewol, was carrying 447 passengers and 27 crew members -- among them, about 320 students.
The group left from the port city of Incheon, just west of Seoul, for a four-day trip to the resort island of Jeju.
Around 9 a.m. local time, the ferry sent out its first distress call. It had begun to list.
A rescued student, Lim Hyung Min, told CNN affiliate YTN that he heard a loud bump. The ferry began to sink after that. Everyone was ordered to don life jackets and jump, he said.
Lim said he jumped into the sea before swimming to a rescue vessel.
"I had to swim a bit to get to the boat to be rescued," he said. "The water was so cold and I wanted to live."
As rescue crews dashed desperately to rescue passengers, the ferry slowly tilted on its side.
With the clock ticking, the 6,800-ton ferry sank. Only its white and blue hull remained above water.
Local media, including CNN affiliate YTN, reported that all students aboard the ship had been rescued. The South Korean Coast Guard hasn't confirmed those accounts.
Passenger Kim Seung Mok said that, despite his efforts and those of others, he couldn't get to several passengers on one of the decks.
"I stayed till the last to rescue people at the hall," Kim told YTN. "But the water was coming in so fast (that) some didn't make it out."
CNN's Euan McKirdy wrote and reported from Hong Kong. Paula Hancocks and journalist Stella Kim in Seoul contributed to this report.