Three crew members of a Chinese fishing boat went missing on Saturday after their vessel collided with an unidentified ship and sank off the coast of a Taiwanese island, the Taiwanese coast guard said.

China claims self-governing Taiwan as part of its territory and relations between the two countries have deteriorated in recent years.

A series of incidents involving fishing boats along the narrow waterway between Taiwan and China have increased tensions.

The latest incident occurred early Saturday when the Chinese-flagged boat “Min Long Yu 60877” sank after colliding with an unidentified vessel about 6.5 nautical miles off the coast of the Kinmen Islands, the Taiwan Coast Guard said in a statement.

“There were seven crew members on board. Four were rescued and three are missing,” it said.

It was said that a patrol boat sent to the area was unable to find the missing crew.

“Those who fell into the sea were not found.”

The statement said the Taiwanese coast guard and their Chinese counterparts would conduct an “enhanced search and rescue operation” in the surrounding waters.

Kinmen County is administered by Taiwan, but is only five kilometers from the Chinese coastal city of Xiamen.

A fatal incident involving a Chinese boat near Kinmen on February 14 sparked a months-long dispute between Taiwan and China.

A boat capsized while being pursued by the Taiwanese coast guard, killing two Chinese crew members. Beijing blamed Taipei for the incident.

After negotiations about the incident, both sides agreed in July that the cause of death was drowning.