Three people were rescued and flown to a hospital with injuries that weren't life-threatening, Jeju coast guard officers said on condition of anonymity because of office rules. Dozens of ships searched the area for survivors.
The 9.8-ton boat, Dolphin, lost communication with another boat on Saturday evening and was found Sunday morning north of the resort island of Jeju. A survivor told Yonhap news agency that the boat quickly capsized because of high waves.
The survivor, identified only by the surname Park, awoke to find the captain telling the passengers to get out as the boat filled with water. Park said survivors clung to the boat for more than 10 hours, but some disappeared in the strong waves before rescuers arrived.
It wasn't clear how many were on board, but most were passengers on a fishing trip, not professional fishermen, one of the coast guard officials said.
A document listed 22 expected passengers, but officials have found that at least four of those listed did not actually board the ship. Also, one of the three survivors wasn't among those listed in the document, Jeju's coast guard chief Lee Pyung-hyun said.
More than 40 coast guard, navy and civilian ships searched the nearby waters, Lee said. The boat had left Chuja Island, northwest of Jeju Island, on Saturday evening to return to a southwestern town on the mainland, before losing communication, Lee said.
South Korea is still dealing with grief and anger over a maritime disaster last year that killed more than 300 people, mostly school children, when a ferry sank off the southern coast. Critics blamed lax government oversight and the country's poor safety culture in part for the sinking.
President Park Geun-hye, heavily criticized for alleged incompetence over last year's ferry sinking, ordered her government to "do everything possible for the search and rescue of the missing" and to keep the public informed about government efforts to deal with this accident, according to her office.
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