The Han Kuang exercises, which started Monday, are held every year across Taiwan to train its armed forces as China ramps up military pressure on the democratic island, which Beijing claims as part of its own territory.

But as Gaemi -- currently categorised as a medium-strength typhoon -- edged closer to Taiwan Tuesday, the island's northeastern regions started seeing heavy rains, with the Central Weather Administration predicting landfall by late Wednesday.

Defence ministry spokesman Sun Li Fang told reporters at an airbase in Hualien that the military will make "flexible adjustments based on the weather conditions in our exercise missions".

"At present, the impact of the typhoon is more obvious in the eastern region and we will make some adjustments to some sea and air exercises due to the typhoon situation," he said on Tuesday.

By nightfall, Gaemi packed sustained wind speeds of 155 kilometres (96 miles) per hour as it headed towards the island's northeastern coast, prompting several cities -- including Taipei -- to announce a typhoon holiday and cancelling schools for Wednesday.

"Tomorrow (Wednesday), please stay home," Taipei mayor Chiang Wan-an said on Facebook.

"Typhoon Gaemi, the first to make landfall this year, continues to intensify... please pay attention to your safety."

Authorities said they were planning to evacuate more than 1,400 people from mountainous areas in the northeast by Tuesday evening, while Taiwanese airline EVA announced the cancellation of more than 20 departing flights from the international airport.

Taiwan experiences frequent tropical storms from May to November, but experts say climate change has increased the intensity of tropical storms, leading to heavy rains, flash floods and strong gusts.

-'Seek immediate shelter' -

The war games this year were a departure from previous iterations, discarding exercises that were "more for demonstration purposes" and opting instead to more realistically simulate an attack from China, the defence ministry had said.

The exercises will also work on decentralising the command structure, while conducting drills around key infrastructure points -- like Taiwan's sea ports, major bridges, and airports.

President Lai Ching-te, dressed in military fatigues, observed earlier in the day as soldiers went through a simulated mass casualty rescue exercise at the Hualien airforce base.

"As guardians of democracy, your efforts are vital for national security & demonstrate our commitment to self-defense," he said on social media platform X.

By afternoon, he arrived in New Taipei City at a port to oversee an elaborate simulation of various emergency situations as part of the annual civilian defence drills -- which run concurrently with Han Kuang.

Lai watched a scenario whereby Chinese missiles had hit the port and its surroundings -- according to an announcer narrating over loudspeaker -- which prompted workers to evacuate civilians.

In Taipei, air raid sirens blared and staff at a train station ushered passengers out, while some people sheltered in a parking lot.

Taipei residents also received an automated text message that said: "(Air Defense Drill) Incoming missile/rocket threat. Seek immediate shelter."

Lai, who is a staunch defender of Taiwan's democracy, is regarded as a "dangerous separatist" by China.

Three days after he was sworn into office in May, China launched war games simulating an encirclement of the island as "punishment" for his inauguration speech, which Beijing said was a "confession of Taiwan independence".

China has said it would never renounce the use of force to bring Taiwan under its control, and maintains a near-daily military presence around the island by sending in warplanes, navy vessels and drones.