At one point a super typhoon and one of the strongest storms in the Pacific this year, Champi is forecast to bring strong winds and torrential rain, and still packing gusts of around 191km/h near its centre, Taiwan's Central Weather Administration says.
The storm's forecast track shows it will pass just off northeastern Taiwan, turn north toward the Chinese coast and eventually move into southern Japan, first passing over its westernmost inhabited island, Yonaguni in Okinawa Prefecture.
Taiwan's government said one person was killed, 94 were injured and almost 1300 people had been evacuated from mountainous areas.
Forecaster Liu Pei-teng told Reuters landfall could not be ruled out if it "stalls, loops, or wobbles from side to side" on approach to Taiwan.
"The storm's wind radius is quite large, among the bigger ones in recent years," Liu said.
"If the storm slows down, the strong winds will affect Taiwan for longer."
Forecasters said the storm's radius was around 320km - large enough to cover most of Taiwan - and weather experts said its impact could last nearly two days.
The transport ministry said all 262 domestic flights were cancelled for Friday, along with 669 international ones.
Taiwan's financial markets closed for the day.
Coastal towns received mobile phone alerts urging residents to seek immediate shelter, while nearly one metre of rain was forecast for northern mountain areas, including around Taipei.
In the northeastern county of Yilan, where the typhoon was forecast to pass close by later on Friday, sandbags, amphibious vehicles and inflatable rescue boats were put on standby.
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