Three Chinese fishermen have died in a fire after their boat was boarded by the South Korean coastguard.
The men, who were suspected of illegal fishing, were caught in the blaze after the coastguard officers threw a "flashbang" or stun grenade into part of their boat where they were hiding.
It is believed they died of smoke inhalation, an official said, and an autopsy has been ordered.
Fourteen other fishermen survived and are being questioned by authorities.
The incident began when a coastguard vessel identified the fishing boat in South Korean waters, and ordered it to stop for inspection.
A coastguard official said the men ignored the commands, and barricaded themselves inside the wheel-house while the boat continued to travel. Officers then fired "flashbang" or stun grenades into the space, after which a fire broke out.
Flashbang grenades are designed to be non-lethal, producing a very loud noise and intense light which temporarily affects vision and hearing. They can also disrupt a person's balance by affecting fluids in the inner ear.
Chinese authorities have requested a full investigation, and South Korea's coastguard has said one is already under way.
Fishing in South Korean waters by Chinese vessels is permitted with the proper authorisation, but illegal fishing has become a point of contention between the two countries in recent years.