MOKPO, South Korea — Lee Gyeong-og, a vice minister for the Public Administration and Security Ministry, said the ocean was 37 meters (121 feet) deep in the area.
The survivors — wet, stunned and many without shoes — were brought to nearby Jindo Island, where medical teams wrapped them in pink blankets and checked for injuries before taking them to a cavernous gymnasium.
As the search dragged on, families of the missing gathered at a nearby dock, some crying and holding each other. Boats circled the sunken ferry into the night, illuminated by red flares.
Angry shouts could be heard when Prime Minister Chung Hong-won visited a shelter where relatives of the missing passengers waited for news. Some yelled that the government should have sent more divers to search the wreckage.
The numbers of passengers, as well as the dead and missing, fluctuated throughout the day. As of early Thursday, South Korean authorities estimated 475 people were on the ferry.
Of that total, there were 325 students and 15 teachers from Danwon High School in Ansan, a city near Seoul. They were headed to Jeju for a four-day trip, according to a relief team set up by Gyeonggi province.
Authorities said the dead included a female member of the crew and two male students. Details on the others were not immediately known. Kang Byung-kyu, a government minister, said 55 people were injured. Coast guard officials put the number of survivors early Thursday at 179.
Many South Korean high schools organize trips for first- or second-year students, 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 Danwon High School, students were sent home early and parents gathered for news about their children. Park Ji-hee, a first-year student, said she saw about a dozen parents crying at the school entrance.
The Sewol, 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, according to the Yonhap news agency.