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

Russia's assault on Ukraine has heightened fears that Beijing might similarly follow through on threats to annex its much smaller and outgunned neighbour.

This year's five-day "Han Kuang" (Han Glory) war games have incorporated lessons from the ongoing European war, simulating "all possible actions" China could take to invade Taiwan, according to the defence ministry.

On Monday, reservists armed with machine guns ran into sandbagged trenches dug under a bridge before getting into firing position, in a drill aimed at blocking enemies from gaining access to the capital Taipei.

"The underground bunkers help cover the troops and ward off the enemy's strike forces," said Su Tzu-yun, a military expert at Taiwan's Institute for National Defence and Security Research.

"They are part of Ukraine's urban warfare."

Stinger missiles, effective against helicopters and low-flying planes, were also deployed in some high-rise buildings in the area, he said.

The highly portable missiles have been invaluable to Ukrainian forces fighting off Russian air power.

Separately, the streets in several northern cities were empty for 30 minutes as part of a civilian air-raid drill, with pedestrians and cars banned after sirens and text-message alerts warned of mock missile attacks.

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

Bill Burns, director of the United States' Central Intelligence Agency, recently said China appeared determined to use force in Taiwan, with Russia's experience in Ukraine affecting its calculations on when and how -- not whether -- to invade.

Last year, Taiwan recorded 969 incursions by Chinese warplanes into its air defence zone, according to a database compiled by AFP -- more than double the roughly 380 in 2020.

The number of sorties has reached more than 600 so far this year.