Southern Taiwan was hit by the storm, which brought torrential rain and ferocious winds, as it rolled past the Batanes island group in the far north of the Philippines -- tearing coconut trees in half -- and headed on towards the Chinese mainland.
At 1800 GMT Severe Typhoon Usagi was estimated to be 500 kilometres (310 miles) southeast of Hong Kong, forcing local carrier Cathay Pacific to warn that all its flights in and out of the city will be cancelled from 6:00 pm (1000 GMT) tomorrow.
In Taiwan's southern Pintung county, storms flooded remote villages, forcing troops to evacuate dozens of people, the state Central News Agency said.
"I thought a tsunami was hitting... I've never encountered this before in my life," said a 60-year-old woman who was scrambling to safety with her pet.
Also Read
Six people were injured in Kinmen, a Taiwan-controlled island off China's southeastern Fujian province, after they were hit by fallen trees, according to the Central Emergency Operation Centre.
A total of 77 domestic and five international flights were cancelled and ferry services suspended, with schools and offices in many parts of Taiwan closed, especially in the south and east, authorities said.
The defence ministry deployed more than 3,000 soldiers to "high-risk" areas and placed 24,000 others on standby.
Nearly 3,000 people had already been evacuated, officials said, as the Central Weather Bureau warned people to expect up to 120 centimetres (47 inches) of rain.