China claims democratically-governed Taiwan as its own territory, over the island's strong objections, and has stepped up military activities near it in recent years, with almost daily incursions into air defence identification zones.

Authorities on both sides sent the rescue boats after a Chinese fishing vessel capsized in the early hours, Taiwan's coast guard said in a statement, adding that two people were missing, though two had been rescued and two bodies retrieved.

Coast guard chief Chou Mei-wu told a parliamentary committee the boats were sent after Chinese authorities sought help, adding that such requests were common, with 119 people rescued in such efforts over the past three years or so.

"The waters are narrow around the Kinmen-Xiamen (area) and co-operation between Taiwan and China is very important," he said, referring to the neighbours' cities that face each other across the strait.

Taiwan sent four coast guard vessels and its Chinese counterpart six to participate in the rescue effort, the coast guard said.

Last month, China's coast guard began regular patrols around the Kinmen islands close to its coast, after two Chinese nationals died while trying to flee Taiwan's coast guard after their boat entered prohibited waters.

The Chinese fishing boat capsized about 1.07 nautical miles west of Taiwan's Dongding island, the coast guard said, with armed forces stationed there also engaging in the rescue, but did not elaborate.

In a statement, Taiwan's Kinmen defense command said it had not received any request from Chinese authorities to search the island, but added that any survivors found would be handed to the coast guard.

Last week, Taiwan's top China policy-making body urged its giant neighbour not to change the "status quo" around the waters there by sending coast guard boats into restricted areas, saying tension should be "controllable".