A Coast Guard vessel enters Jeju Harbor at 12:30 a.m. on Monday, carrying the body of a crewmember who died when a fishing boat sank on Friday. (Yonhap)

The Coast Guard on Monday expanded the area in which it is searching for the crew members who went missing last week when a fishing boat sank off the coast of Jeju Island, as another body found the day before brought the death toll to four.

The Jeju Coast Guard said 47 boats and eight aircraft were mobilized in the day's search for the 10 missing crew members across an area measuring 64 kilometers by 28 kilometers. The search continued for a fourth straight day in the waters near the wreckage area some 22 kilometers northwest of Biyangdo Island.

The Coast Guard has been collaborating on the search with the Navy and the civilian sector, including the Navy's submarine rescue ship Cheonghaejin (ASR-21) and its remotely operated vehicles. The bodies of the two missing crewmen found on Saturday and Sunday were discovered by the Cheonghaejin's ROVs.

The search for the 27 crew members of the 129-ton Geumseon has been going on since the vessel sank in the early hours of Friday. Fifteen of them were pulled out of the water, but two were pronounced dead upon arrival at a hospital in Jeju City.

All four of the confirmed dead were Korean nationals. The crew of the Geumho comprised 16 Koreans and 11 Indonesians, with eight Koreans and two Indonesians still unaccounted for as of Monday afternoon.

It was revealed that the boat sank while the crew were transferring their catch to another vessel. The fishing boat left Seogwipo harbor on the southern part of Jeju Island shortly before noon Thursday.

Officials believe that a majority of the crew were not wearing life vests at the time of the accident, and all but two of them were on the deck when the boat sank.