The crew of a Chinese trawler and a South Korean patrol ship have clashed, leaving one fisherman dead and two missing, South Korean officials say.
The clash reportedly happened as the coast guards tried to prevent Chinese boats from fishing illegally off South Korea's west coast.
Video filmed by the coast guard shows officers fighting with fishermen wielding metal bars.
Four coast guard officers were injured, reports say.
About 50 Chinese fishing boats were in waters off the South Korean city of Gunsan at the time of the clash, coast guard spokesman Ji Kwan-tae said, according to the Associated Press.
Mr Ji said one of the boats intentionally struck the patrol ship to try to allow the others to sail back into their waters - but the boat sank after the impact.
At least eight men were rescued from the sea, but one later died.
More guard boats and helicopters were dispatched to try to locate two missing fishermen. China has also reportedly sent a rescue boat to the area.
Scores of Chinese fishing boats are captured for illegal fishing every year, the South Korean coast guard says.
Chinese vessels appear to be going further afield to feed growing domestic demand for seafood.
In September, a confrontation between two Japanese patrol boats and a Chinese trawler in the East China Sea provoked a bitter diplomatic spat.
The latest clash comes amid heightened tension on the Korean peninsula and in the waters around it.
Last month North Korea - incensed by live-fire military exercises conducted close to its coast by the US and South Korea - shelled a South Korean island.
It has threatened fresh action if a planned new drill takes place.