"China will firmly defend its national sovereignty and territorial integrity," foreign ministry spokeswoman Mao Ning said, as the island's military launched combat readiness drills.

Taiwan's defence ministry said it also spotted Chinese coast guard vessels and that Beijing's People's Liberation Army (PLA) had restricted the airspace off the Chinese coast.

There has been intense speculation about the possibility of China launching military drills in response to Taiwanese President Lai Ching-te's trip to the Pacific which included stopovers in Hawaii and Guam.

Asked about the possibility of drills around the island and the claims by Taipei, Mao insisted: "Taiwan does not have a ministry of defence."

"Taiwan is an inalienable part of China's territory and the Taiwan issue is China's internal affair," Mao said.

Taiwan regards itself as a sovereign nation with its own government, military, and currency.

But Beijing insists the island is part of its territory and has not ruled out using force to bring it under its control.