Taiwan has arrested a Chinese man who sailed a speedboat into a harbor at the mouth of a river leading into Taipei for illegal entry, the Taiwanese coast guard said on Monday.

Taiwan keeps a close watch on its waters and air space, given tensions with China, which views the democratically governed island as its own territory, a claim Taipei rejects.

Taiwan's coast guard said a suspicious vessel was spotted on Sunday morning six nautical miles (11 km) off the coast of Tamsui in northern Taiwan. After entering the Tamsui River, which leads to downtown Taipei, the boat collided with other vessels at a ferry terminal.

A lone Chinese man on the vessel was arrested on suspicion of violating Taiwan's entry and exit laws, the coast guard said.

It did not say what his motive was.

China's Taiwan Affairs Office did not answer calls seeking comment on Monday, a holiday in both China and Taiwan.

In March, two Taiwanese fishermen strayed into Chinese waters near the Taiwan-controlled Kinmen islands, which sit next to China's coast. One, a Taiwanese military officer, remains in detention in China, while the other was released soon after.

During the height of the Cold War, people from both sides of the Taiwan Strait would, on occasion, cross to the other side seeking to defect by air or water, but such events are rare now.

(Reuters)

A police boat with a Taiwan flag sails at the Port of Taipei in Taipei, Taiwan. (Reuters)

Taiwan arrests Chinese man who took speedboat into Taipei harbor