China has started military exercises with ships and aircraft near Taiwan, just days after the self-ruled democratic island marked its National Day.

The exercises, dubbed Joint Sword-2024B, began early on Monday and were a “stern warning to the separatist acts of ‘Taiwan Independence’ forces”, said Beijing, which claims the island as its own.

Captain Li Xi, the spokesman for the Chinese military’s Eastern Theatre Command, said the drills were focussed on “sea-air combat-readiness patrol, blockade on key ports and areas” and would also involve an “assault on maritime and ground targets”.

The drills, he added, were a “legitimate and necessary operation for safeguarding state sovereignty and national unity”, and gave no date for their conclusion.

Taiwan’s Ministry of Defence expressed its strong condemnation of China’s “irrational and provocative actions” and said it had “dispatched appropriate forces to respond accordingly to protect freedom and democracy, and defend the sovereignty” of Taiwan.

As of 8am (00:00 GMT), it said some 25 PLA aircraft and a total of 11 ships, including seven from the navy, were found operating around Taiwan.

“I would like to reassure my compatriots that the government will continue to defend the democratic and free constitutional system, protect democratic Taiwan, and safeguard national security,” he wrote on Facebook.

In recent years, China has stepped up its military activity around Taiwan, which it claims as its own. The latest drills come just days after Lai gave his first National Day address on October 10, promising he would resist any “annexation or encroachment” and that Beijing had no right to represent the island’s 23 million people.