A group of crew members of a fishing vessel that sank in waters off Yeosu, 316 kilometers south of Seoul, wait to be rescued by the Coast Guard aboard a life raft on Feb. 9, in this photo provided by the Coast Guard. Yonhap

A fishing trawler with 14 crew members on board sank in waters off Korea's southern coast early Sunday, leaving four people dead and five others missing, officials said. Rescue efforts were under way.

The Coast Guard said it has located the 139-ton vessel at a depth of about 80 meters under the sea, hours after the ship was reported missing at 1:41 a.m. in waters about 17 kilometers east of the island of Habaek, near Yeosu, some 315 km south of Seoul.

One of the missing crew members was discovered inside the vessel, the Coast Guard said, without confirming whether he was alive or dead.

That leaves five people still unaccounted for. Four South Koreans have died, including the vessel's 66-year-old captain, while four other crew members survived.

Eight South Koreans, three Vietnamese and three Indonesians were aboard the vessel.

Authorities had initially rescued eight crewmen — five of whom were found aboard a life raft and the rest drifting in the freezing waters. But four of them, including the captain, were later pronounced dead.

Two Vietnamese and Indonesian crew members survived.

The two rescued Indonesians have been moved to the Coast Guard's office in Yeosu to be interviewed about the accident, while the Vietnamese nationals are being treated at a nearby hospital after showing signs of hypothermia.

Coast Guard officials transport a rescued crew member of a fishing vessel that sank in waters off Yeosu, 316 kilometers south of Seoul, Feb. 9, in this photo provided by the Coast Guard. Yonhap

The Coast Guard said the vessel appears to have capsized after heavily tilting to its left side based on remarks from the rescued Vietnamese crew members.

"Excluding three people inside the ship, all 11 other crew members jumped into the sea," it said in a briefing.

Despite poor weather conditions, the Coast Guard considers it unusual for a vessel of over 100 tons to have capsized in the 2.5-meter waves at the time, and is investigating the exact cause of the incident.

The fishing trawler was part of a group of four other fishing vessels but it reportedly did not send out a distress signal, leading the Coast Guard to suspect the sinking took place unexpectedly.

The vessel departed from Gamcheon port in Busan, some 320 km southeast of Seoul, on Saturday to catch fish in waters near the southwestern island of Heuksan, South Jeolla Province.

A total of 24 patrol ships, four Navy vessels, 13 aircraft and other civilian and agency ships have been deployed to search for the missing crew members.

During search efforts in the morning, a Coast Guard high-speed boat capsized due to high waves but all six on board were rescued by another Coast Guard vessel. (Yonhap)