Beijing has not ruled out using force to bring Taiwan under its control and Monday's drills represent its fourth round of large-scale war games in the past two years.

China's drills come days after US Secretary of State Antony Blinken warned Beijing against taking action in response to a speech by Taiwanese President Lai Ching-te during the island's National Day celebrations.

Lai, who took office in May, has been more outspoken than his predecessor Tsai Ing-wen in defending Taiwan's sovereignty, angering Beijing, which calls him a "separatist".

Taiwan condemned the latest exercises as "irrational and provocative" and said it has dispatched "appropriate forces" in response.

AFP journalists near the Hsinchu air force base, in the north of Taiwan, saw six fighter jets take off on Monday.

Beijing said its exercises served as a "stern warning to the separatist acts of 'Taiwan Independence' forces".

The drills, dubbed Joint Sword-2024B, "test the joint operations capabilities of the theater command's troops", said Captain Li Xi, spokesman for the Chinese military's Eastern Theater Command.

They are taking place in "areas to the north, south and east of Taiwan Island," he said.

The drills are "focusing on subjects of sea-air combat-readiness patrol, blockade on key ports and areas", Li said.

They also practised an "assault on maritime and ground targets" and "joint seizure of comprehensive superiority".

- China coast guard 'inspections' -

China's coast guard was also dispatched to conduct "inspections" around the island.

A diagram released by the coast guard showed four fleets encircling Taiwan and moving in an anticlockwise direction around the island.

The coast guard of the eastern province of Fujian -- the closest area on the mainland to the self-ruled island -- also said it was conducting "comprehensive law enforcement patrols" in waters near the Taiwan-controlled Matsu islands.

Taiwan said four "formations" of China coast guard ships were patrolling around the island, but they had not entered its prohibited or restricted waters.

China has ramped up military activity around Taiwan in recent years, sending in warplanes and other military aircraft while its ships maintain a near-constant presence around the island's waters.

"In the face of enemy threats, all officers and soldiers of the country are in full readiness," Taiwan's defence ministry said Monday.

"We are determined and confident to ensure national defence security."

In his speech on Thursday, Lai vowed to "resist annexation" of the island, and insisted Beijing and Taipei were "not subordinate to each other".

China warned after the speech that Lai's "provocations" would result in "disaster" for the people of Taiwan.

Beijing on Monday said the drills were "a legitimate and necessary operation for safeguarding state sovereignty and national unity".

Beijing's state broadcaster CCTV released a video warning: "the greater the provocation, the tighter the reins".

Taiwan's defence ministry said Monday that 25 Chinese aircraft and seven navy vessels were detected around island in the 26 hours to 8:00 am (0000 GMT).

- 'Feel a bit numb' -

Lieutenant Colonel Fu Zhengnan, a researcher at the Chinese Academy of Military Sciences, said in a video shared by state media that the drills could "switch from training to combat at any time."

"If Taiwan separatists provoke once, the PLA's operation around the island will make their first move," Fu said, referring to China's People's Liberation Army.

During morning rush-hour in Taipei, people appeared to be largely unperturbed by the latest drills.

"I won't panic too much because they quite often have drills," 34-year-old engineer Benjamin Hsiao told AFP.

"It's not the first time in recent years anyway, so I feel a bit numb."

The current dispute between China and Taiwan dates back to a civil war in which the nationalist forces of Chiang Kai-shek were defeated by Mao Zedong's communist fighters and fled to Taiwan in 1949.

Lai's Democratic Progressive Party has long defended the sovereignty and democracy of Taiwan, which has its own government, military and currency.

Beijing has sought to erase Taipei from the international stage, blocking it from global forums and poaching its diplomatic allies.

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