Coast Guard officers undertake a search operation for missing crew members in waters off Jeju, Friday. Yonhap

Two people died and 12 others remained missing after a fishing boat sank off the southern island of Jeju on Friday, with a search under way, the Coast Guard said.

The 129-ton Geumseong was carrying 27 crew members — 16 Koreans and 11 foreigners – when the Coast Guard received a distress call at 4:33 a.m. that the boat was sinking 24 kilometers off Jeju's Biyang Island.

Of the 27, 15 were rescued, including two who were found in a state of cardiac arrest, and taken to nearby hospitals. The two, both Koreans, were later pronounced dead.

The 12 missing are 10 Koreans and two foreigners.

The rescued crew members said they were transferring their catch to another vessel when the boat suddenly capsized and began to sink, according to the Coast Guard. The boat is now completely underwater.

Rescued crew members are taken to a nearby port after their fishing boat sank off the coast of Jeju Island, Friday, in this photo provided by the Jeju firefighting and safety headquarters. Yonhap

President Yoon Suk Yeol was briefed on the sinking and instructed relevant agencies, including the Coast Guard and the defense and oceans ministries, to mobilize all available resources and personnel to rescue the missing, according to presidential spokesperson Jeong Hye-jeon.

He also called for ensuring the safety of the rescue workers.

The Coast Guard has sent 18 vessels and five aircraft to the scene to take part in search and rescue operations. Six Navy vessels — including a destroyer, a frigate and a salvage ship — were also mobilized, along with the Navy's P-3 maritime patrol aircraft and Lynx helicopter.

The Geumseong, which catches mackerel and sardines, left Seogwipo harbor on Jeju's coast shortly before noon Thursday. At the time of the accident, two people, including a cook, were inside the boat, while most of the other crew members were working on the deck, presumably without wearing life vests, the Coast Guard said.

The Jeju Coast Guard plans to hold a press conference on the sinking at 2 p.m. (Yonhap)