Cities across northern Taiwan ordered cars off roads and people to stay indoors on Monday for an annual air-raid exercise as the island steps up preparations in the event of a Chinese attack amid rising military threats from Beijing.
Sirens sounded at 1.30pm (0530 GMT) for the mandatory street evacuation drills, which effectively shut towns and cities including its capital Taipei for 30 minutes.
An "air raid alert", asking people to evacuate to safety immediately, was sent via text message.
"When you receive the text message, please be aware of the wordings such as 'test' and 'drill' and stay calm," Taiwan President Tsai Ing-wen said in a reminder to the public on Facebook about an hour before the exercise named Wan An, which means everlasting peace.
China, which views democratically governed Taiwan as its territory, has been staging regular exercises around the island for the past three years, to pressure Taipei to accept Beijing's claim of sovereignty despite the island's strong rejections.
In the bustling shopping district of Ximending in Taipei, some shops pulled down their shutters and police directed passersby and vehicles including food delivery drivers on motorcycles to move to the side of the road and seek shelter.
Tourists with luggage were seen taking shelter in a subway station, some shocked and not sure what had happened.
"I heard the siren and I was worried, not knowing what happened especially we are foreigners in a foreign country," said Lee Jang Ho, a tourist from South Korea.
Among the various drills carried out by authorities in Taipei, some citizens were instructed to seek shelter in basement parking lots with their hands covering their eyes and ears while keeping their mouths open - to minimise the impact of blast waves from missiles.
Sirens sounded 30 minutes later to give the all-clear. Other parts of Taiwan, where periodic air-raid drills are required by law, will carry out street evacuation drills this week.
Beijing has stepped up its warnings against a trip to the US by Taiwan vice president and presidential frontrunner William Lai next month, while the top US diplomat in Taipei urged China not to take "provocative" action in response to the brief transits.