Democratic Taiwan lives under constant threat of being invaded by China, which views the self-ruled island as part of its territory to be seized by force if necessary.

On the second day of the island's largest annual war drills, Tsai, dressed in military fatigues, boarded the Kee Lung class destroyer to supervise a live-fire drill off Taiwan's eastern coast.

Fighter jets and warships set off various types of missiles aimed at intercepting "a group of enemy ships", the military said.

Anti-submarine rockets and depth bombs were also discharged and a Dutch-built Sword Dragon class submarine practised an emergency ascent, it added.

"The precise and solid exercise carried out by everyone just then demonstrates the capabilities and determination of the Republic of China's military to protect our home and defend our country," Tsai said in a message broadcast to the ship, using Taiwan's formal name.

Beijing's sabre-rattling has increased considerably since Tsai took office in 2016, as she rejects its stance that the island is part of China.

This year's five-day "Han Kuang" (Han Glory) war drills have incorporated lessons from Russia's invasion of Ukraine, which has heightened fears of a Chinese assault on the island.

CIA chief Bill Burns said last week Beijing appeared determined to use force in Taiwan, with Russia's experience in Ukraine affecting its calculations on when and how -- not whether -- to invade.

The Taiwan Strait, the narrow waterway separating the island from mainland China, is often a flashpoint between the two sides, with Beijing maintaining it is not international waters.