Taiwan's coast guard said four Chinese coast guard boats on Saturday morning entered the restricted waters of Taiwan-controlled Kinmen islands, which hug the Chinese coast. It said the Chinese boats stayed just over an hour after Taiwan authorities asked them to leave.

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

"You have entered our country's restricted waters. Please turn around immediately," a Taiwan official said via radio in a broadcast message to their Chinese counterparts, according to footage released on Saturday by Taiwan's coast guard.

The footage shows a Taiwan coast guard boat tracking the movement of two Chinese ships in the near distance.

"The move has seriously impacted traffic and safety. To avoid triggering naval incidents we urge them to stop such behaviours," Taiwan's coast guard said in a statement.

There was no immediate comment from China's coast guard, which does not have publicly available contact details.

China's coast guard conducted patrols near the Kinmen Islands on Friday as well, with four Chinese coast guard boats being warned away by their Taiwanese counterparts, according to Taiwan's official Central News Agency.

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

Taiwan dispatched coast guard boats on Thursday to join a rescue mission at China's request after a Chinese fishing vessel capsized near the Kinmen islands. Taiwan's government has stressed the importance of co-operation between Taiwan and China amid the heightened tensions.

On Friday, Taiwan also sent several boats at China's request to help search for a Chinese fisherman who went overboard near the Taiwan-controlled Matsu islands, in the northern end of the Taiwan Strait.

A senior Taiwan security official, who requested anonymity due to the sensitivity of the matter, told Reuters that Beijing is sending out "confusing" messages by continuing its harassment of Taiwan, while also asking for Taipei's assistance on dealing with maritime incidents.

The official said the latest moves by the Chinese coast guard in Kinmen "did not carry substantial security threats" but complicated the situation there.

"We are clueless," the official said. "We tried to save their fishermen yesterday and today they are baring their teeth and claws."

Last week, Taiwan's top China policy-making body urged its giant neighbour not to change the "status quo" in waters near Kinmen by sending coast guard boats into restricted areas.