A Chinese fishing boat capsized in waters off the southwestern city of Gunsan on Wednesday, leaving three crew members unconscious and three others missing, Coast Guard officials said.

According to the Coast Guard, the 239-ton vessel capsized shortly after midnight in waters 124 kilometers southwest of Gunsan's Eocheong Island.

Of the 15 crewmen aboard the ship, eight have been rescued by the Coast Guard and another Chinese boat that was fishing alongside the capsized vessel.  

Four more crewmen were later found adrift on the sea and rescued, but three of them were unconscious, officials said. The other was in stable condition.

A search is under way to rescue the other three crewmen who remain unaccounted for.

A team of four patrol ships and two aircrafts were additionally dispatched to back up the search operation in cooperation with a fishery inspection boat and two Chinese fishing boats at the scene, officials said.

But rescuers were having difficulties due to high waves of up to three meters and bad weather.

"After designating the 20-kilometer radius of the accident scene as the scope of search, we are looking for those missing people," an official at the Coast Guard's Gunsan office said.

The capsized Chinese boat was fishing in the South Korean exclusive economic zone after getting permission, the officials said. (Yonhap)