Taiwan's Coast Guard said three crewmen from a Chinese fishing boat went missing on Saturday after their boat sank off the shore of an island in Taiwan after colliding with an unidentified vessel.

Taiwan's Coast Guard Administration stated in a statement that the most recent incident happened early on Saturday when the Chinese-flagged boat Min Long Yu 60877 sank after colliding with an unidentified vessel approximately 6.5 nautical miles, off the coast of the Kinmen Islands.

"There were seven crew members on board. Four were rescued and three were missing," it said, adding that the missing crew was not located by a patrol boat dispatched to the region.

"Those who fell into the sea were not found."

According to the statement, "an expanded search and rescue" was being conducted in nearby waters by Taiwan's Coast Guard and its Chinese counterparts.

Read next: Taiwan demands China release apprehended fishing boat

Although Kinmen County is under Taiwanese administration, it is only five kilometers (three miles) from Xiamen, a seaside city in China.

The Kinmen Islands, administered by Taipei but situated just five kilometers (three miles) from the Chinese mainland, have been the focus of recent tensions.

It is worth noting that new maritime rules issued by China on June 15 allow the China Coast Guard to detain foreigners for trespassing in Chinese-claimed territories in the South China Sea.

These regulations have sparked outrage in the region, as governments closely allied with the United States, such as those in the Philippines and Taiwan, see the new regulation as threatening. 

This is not the first incident of its kind. In response to a series of deadly fishing incidents, including one that resulted in sharp exchanges of blame, the Chinese Coast Guard has increased its patrols around Taiwan's Kinmen lslands in recent months.