A Coast Guard helicopter crashed near an island off South Korea's southwest coast Friday while it was trying to transport an emergency patient from the island, firefighter officials said.

The helicopter, with a total of four passengers on board, was trying to land near a seawall on Gageodo island when it crashed into the sea at 8:27 p.m., they said.

The helicopter left the southern city of Mokpo about 50 minutes earlier toward the island on a mission to transport the patient to an inland hospital, according to the officials.

A heavy sea fog reported in the area may have been the cause of the accident, they noted. A rescue vessel arrived at the accident scene as the authorities kicked off search and rescue efforts, but the fate of the four passengers, including two pilots, is still not known, the officials said. (Yonhap)