Typhoon Koinu, travelling westward from the Pacific, was strengthening as it moved toward Taiwan, meteorologists on the island said Monday.
The storm was expanding in size and was expected to make landfall by Thursday morning, they said.
The typhoon was moving northwest with sustained winds of 144 kph (89 mph) and gusts of up to 180 kph (112 mph), according to Taiwan's Central Weather Bureau.
Forecasters predict the centre of the storm will hit the island's southern cities, while bringing heavy rains to the east coast including the city of Taitung.
Typhoon Koinu, also known as Typhoon Jenny, is “forecast to steadily intensify throughout the forecast period and may reach its peak intensity tomorrow,” said a typhoon bulletin from the Philippines weather bureau.
The storm, travelling at 15 kph (9.3 mph), will bring rains to Taiwan starting Tuesday with its outer bands.
Authorities are expected to issue a sea warning Monday night, local media reported, as the storm could create large waves and rough seas.
The storm is also bringing heavy rains to parts of the northern Philippines from Monday to Tuesday, mainly in Cagayan province, which is just south of Taiwan.
Typhoon Haikui hit Taiwan in early September, the first typhoon to make landfall in years. It uprooted trees and damaged cars, and injured dozens, but did not cause any catastrophic damage.