The weather system was still a tropical depression off the northern Philippines, storm-tracker Tropical Storm Risk said on its web site www.tropicalstormrisk.com. But Taiwan's Central Weather Bureau said on its website www.cwb.gov.tw the storm would strengthen into a typhoon named Kalmaegi and was set to reach Taiwan as early as Wednesday.
The storm, presently with sustained winds of 65 kph (40 mph) and gusts of 90 kph, is expected to reach southeast China by the weekend, the bureau said.
Typhoons regularly hit China, Taiwan, the Philippines and Japan from August until the end of the year, gathering strength from the warm waters of the Pacific or the South China Sea before weakening over land.
Krosa, the last typhoon to hit Taiwan, kept people indoors as work and classes were cancelled. Three people were injured in the early October storm.
(Reporting by Ralph Jennings; Editing by David Fogarty)