Rescue workers are continuing the search for 12 missing crew members of a fishing boat that sank in waters off Jeju Island early on Friday. 

The Jeju branch of the Coast Guard said it is mobilizing all available resources for the search, as the first 24 hours are considered crucial with water temperatures in the area at 22 degrees Celsius or about 72 degrees Fahrenheit.

As of Friday afternoon, 43 vessels and 13 aircraft were combing the area. 

The regional Coast Guard received a distress call around 4:31 a.m. on Friday, indicating that the 129-ton Geumseong vessel was sinking 24 kilometers northwest of Jeju’s Biyang Island.

The boat was carrying 27 crew members, 16 South Koreans and eleven Indonesians. 

Fifteen crew members were rescued and taken to a nearby hospital, but two of them, both South Koreans, were later pronounced dead. 

The Coast Guard formed an investigation team to find out the exact cause of the accident. 

The team is also looking into possible violations of the Serious Accidents Punishment Act.