A fishing boat capsized in waters off the southeastern city of Tongyeong early Saturday, with three of the nine sailors listed with the vessel found unconscious inside and later pronounced dead, while the rest are missing.

According to the Coast Guard, the 20-ton-class vessel turned over some 68 kilometers south of Tongyeong's Yokji Island at around 6:30 a.m., after it departed from Hallim port on Jeju Island Thursday morning.

Another boat that worked with the capsized vessel in a fishing operation reported to authorities that it had lost contact at around 6 a.m., after which the boat in question was discovered upside down some 40 minutes later.

One South Korean and two Indonesians were found unconscious, while six others - one South Korean and five Indonesians - are unaccounted for. The three found inside the vessel were taken to a nearby hospital but were later pronounced dead.

The Coast Guard has deployed 12 patrol vessels, four naval ships and six aircraft for a search and rescue operation.