JEJU ISLAND (Yonhap News) ― Maritime police on this resort island said Saturday they have seized three Chinese fishing boats for poaching and obstruction of duty in South Korean waters.

Jeju maritime police first seized a Chinese boat which was illegally fishing inside South Korea’s exclusive economic zone off Jeju at around 4:25 a.m. Soon after, 25 Chinese trawlers approached a South Korean maritime police vessel in the area to demand the release of the seized Chinese boat.

As the Chinese boats ignored repeated warnings to stay away, Jeju maritime police mobilized 12 patrol vessels and two helicopters to crack down on them and captured two more trawlers, the officials said.

It’s unknown how many Chinese fishermen were under custody.

Violent clashes often occur between South Korean maritime police and Chinese fishing boats illegally operating in South Korean waters. In recent clashes, one officer lost his life. In March of this year, a 63-ton Chinese boat intentionally rammed into a 3,000-ton Coast Guard patrol vessel off the west coast, injuring several officers.