Last Updated Apr 16, 2014 12:05 PM EDT
MOKPO, South Korea -- A ferry carrying 462 people, mostly high school students on an overnight trip to a tourist island, sank off South Korea's southern coast on Wednesday, leaving more than 280 people missing despite a frantic, hours-long rescue by dozens of ships and helicopters. At least four people were confirmed dead and 55 injured.
The high number of people unaccounted for - likely trapped in the ship or floating in the ocean - raised fears that the death toll could rise drastically, making it one of South Korea's biggest ferry disasters since 1993, when 292 people died.
CBS News correspondent Seth Doane reports that a U.S. Navy ship was on standby in the area ready to aid the rescue effort.
Hundreds of parents desperately boarded buses to be taken to the area near where the ferry sank.
A mother of an 18-year-old student said, "I felt like my heart stopped. I can't describe the feeling with one word. I can't even talk about it."
One student, Lim Hyung-min, told broadcaster YTN after being rescued that he and other students jumped into the ocean wearing life jackets 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, adding that some people were bleeding. Once he jumped, the ocean "was so cold. ... I was hurrying, thinking that I wanted to live."
Local television stations broadcast live pictures of the ship, Sewol, listing to its side and slowly sinking as passengers jumped out or were winched up by helicopters. At least 87 vessels and 18 aircraft swarmed around the stricken ship. Rescuers clambered over its sides, pulling out passengers wearing orange life jackets. But the ship overturned completely and continued to sink slowly. Within a few hours only its blue-and-white bow stuck out of the water.
Some 160 coast guard and navy divers searched for survivors inside the ship's wreckage a few miles from Byeongpung Island, which is not far from the mainland and about 290 miles from Seoul. Cho Man-yong, a coast guard spokesman, said 16 divers approached the ferry Wednesday night but failed to get inside because the current was too strong. He said the water was very muddy and visibility was poor, but navy and coast guard divers planned to make another approach after midnight.
"We cannot give up," said South Korean President Park Geun-hye, after a briefing in Seoul with officials. "We have to do our best to rescue even one passenger."
Those rescued - wet, stunned and many without shoes - were brought to nearby Jindo Island, where medical teams wrapped them in pink blankets and checked them for injuries before settling them down on the floor of a cavernous gymnasium hall.
The ship had set off from Incheon, a city in South Korea's northwest and the site of the country's main international airport, on Tuesday night for an overnight, 14-hour journey to the tourist island of Jeju.
Three hours from its destination, the ferry sent a distress call at about 9 a.m. Wednesday after it began listing to one side, according to the Ministry of Security and Public Administration. Officials didn't know what caused it to sink and said the focus was still on rescuing survivors.
Lee Gyeong-og, a vice minister for South Korea's Public Administration and Security Ministry, said 30 crew members, 325 high school students, 15 school teachers and 89 non-student passengers were aboard the ship.
Authorities said the dead included a female crew member and two male high school students. A coast guard officer confirmed a fourth fatality but had no immediate details about it.
Kang Byung-kyu, a government minister, said 55 people were injured.
Coast guard officials said late Wednesday that they had found one more person who had been unaccounted for - a 5-year-old girl who was staying alone at a hospital after being rescued - raising the number of survivors to 175. A total of 283 people remained missing.
Yonhap news agency said the 480-foot-long ship, which travels twice a week between Incheon and Jeju, was built in Japan in 1994 and could carry a maximum of 921 people, 180 vehicles and 152 shipping containers.
The water temperature in the area was about 54 Fahrenheit, cold enough to cause signs of hypothermia after about 1 1/2 hours of exposure, according to an emergency official who spoke to The Associated Press on condition of anonymity citing department rules. Lee, the vice minister, said the ocean is 121 feet deep in the area.
Passenger Kim Seong-mok told YTN that he was certain that many people were trapped inside the ferry as water quickly rushed in and the severe tilt of the vessel kept them from reaching the exits. Some people urged those who couldn't get out to break windows.
Kim said that after having breakfast he felt the ferry tilt and then heard it crash into something. He said the ferry operator made an announcement asking that passengers wait and not move from their places. Kim said he didn't hear any announcement telling passengers to escape.
The students - about half of them boys and half girls- are from Danwon High School in Ansan city, which is near Seoul, and were on their way to Jeju island for a four-day trip, according to a relief team set up by Gyeonggi province, which governs the city. There are faster ways to get to Jeju, but some people take the ferry from Incheon because it is cheaper than flying. Many South Korean high schools organize trips for students in their first or second years, and Jeju is a popular destination. The students on the ferry were in their second year, which would make most of them 16 or 17.
At the high school, students were sent home and parents gathered for news about the ferry.
Park Ji-hee, a first-year student, said she saw about a dozen parents crying at the school entrance and many cars and taxis gathered at the gate as she left in the morning.
She said some students in her classroom began to cry as they saw the news on their handsets. Teachers tried to soothe them, saying that the students on the ferry would be fine.
The Maritime Ministry said the two previous deadliest ferry disasters were in 1970 when 323 people drowned and in 1993 when 292 people died.