The two days of drills are part of an escalating campaign of intimidation by China that has seen it carry out a series of large-scale military exercises around Taiwan in recent years.

The drills come after Lai Ching-te was sworn in as Taiwan's new president this week and made an inauguration speech that China denounced as a "confession of independence".

As the drills got underway, China's military said they would serve as "strong punishment for the separatist acts of 'Taiwan independence' forces".

Foreign ministry spokesman Wang Wenbin then delivered a warning that included language more commonly used by China's propaganda outlets.

"Taiwan independence forces will be left with their heads broken and blood flowing after colliding against the great... trend of China achieving complete unification," Wang told reporters.

The United Nations called for all sides to avoid escalation, while the United States -- Taiwan's strongest ally and military backer -- "strongly" urged China to act with restraint.

- 'Defend freedom' -

China -- governed by the Communist Party since 1949 -- claims Taiwan as part of its territory and has vowed to bring the democratic island under its rule, by force if necessary.

Thursday and Friday's drills -- codenamed "Joint Sword-2024A" -- involve aircraft and ships surrounding the island to test their combat capabilities, China's People's Liberation Army (PLA) said.

Taiwan responded by deploying air, ground and sea forces, with the island's defence ministry vowing to "defend freedom".

President Lai said he would "stand on the front line" to defend Taiwan in a speech on Thursday afternoon, without directly referring to the ongoing drills.

"Faced with external challenges and threats, we will continue to defend the values of freedom and democracy, and safeguard peace and stability in the region," he said.

China has repeatedly branded Lai a "dangerous separatist" who would bring "war and decline" to the island.

Beijing was further incensed with his inauguration speech on Monday in which he hailed a "glorious" era for Taiwan's democracy.

The drills, which began on Thursday morning, are taking place in the Taiwan Strait and to the north, south and east of the island, as well as areas around the Taipei-administered islands of Kinmen, Matsu, Wuqiu and Dongyin.

China's military put out a series of posters touting what it called its "cross-strait lethality". They featured rockets, jets and naval vessels next to blood-stained text.

"The weapon aimed at 'Taiwan independence' to kill 'independence' is already in place," it declared.

As of around 8:00 pm (1200 GMT), Taipei's defence ministry said 49 jets and planes had been detected since the drills began at 7:20 am. Thirty-five of the aircraft had crossed the median line bisecting the Taiwan Strait.

UN Secretary-General Antonio Guterres called for all sides to "refrain from acts that could escalate tensions in the region," his spokesman said.

US President Joe Biden has previously said he does not support Taiwan's independence but also that he would back sending forces to defend the island. The official US position on intervention is one of ambiguity.

"We strongly urge Beijing to act with restraint," a US spokesperson said, adding China's actions "risk escalation and erode longstanding norms that have maintained regional peace and stability for decades."

- Economic blockade -

Beijing, which split with Taipei at the end of a civil war 75 years ago, regards the self-ruled island as a renegade province with which it must eventually be reunified.

China has stepped up pressure on the island of 23 million people, periodically stoking worries about a potential invasion.

A Chinese military expert told CCTV that the drills were partly aimed at rehearsing an economic blockade of the island.

Zhang Chi, a professor at Beijing's China National Defense University, said the drills aimed to "strangle" Taiwan's critical Kaohsiung port to "severely impact" its foreign trade.

They would cut off "Taiwan's lifeline of energy imports" as well as "block the support lines that some US allies provide to 'Taiwan independence' forces", he added.

The last time China announced similar military exercises around Taiwan was in August last year after Lai, then vice president, stopped over in the United States on a visit to Paraguay.

They followed April drills that simulated the encirclement of the island, launched after Lai's predecessor Tsai Ing-wen met then-US House Speaker Kevin McCarthy in California.

World powers are keen to see as much stability as possible between China and Taiwan, not least because of the vital role the island plays in the global economy.