Taiwan evacuated more than 1,000 tourists from an island and deployed troops on Tuesday in preparation for the possible arrival of Tropical Storm Trami.
The Central Weather Bureau said the storm, 710 kilometres east-southeast of Taipei at 6am GMT, could bring heavy rain even if it did not make landfall.
The storm, with gusts up to 126 kilometres per hour, was moving west north-west at a speed of 22 kilometres per hour. Officials at the bureau said the impact may be felt mostly from Wednesday night through Thursday morning.
In reaction to the warning, ferries operating between the southeastern city of Taitung and Green Island evacuated 1,700 tourists.
Television images showed hundreds of fishing boats packing Suao, a fishing port in the northeast county of Ilan that is likely to bear the brunt of the storm.