The warning, issued by the National Disaster Reduction Commission and the Civil Affairs Ministry, urged local authorities to prepare for emergencies and minimize possible losses caused by the 19th typhoon to strike China so far this year, China's state-run Xinhua news agency reported.
Usagi was about 388 miles south of Taiwan's Cape Eluanbi Friday and forecast to pick up strength as it moved on a northwesterly track, the National Meteorological Center said.
Authorities in Taiwan said the storm was forecast to hit the island Saturday. Usagi was expected to make landfall in Guangdong province Sunday.
Severe rainstorms were forecast Friday and Saturday for the Taiwan's eastern and southern areas, forecasters said. The heavy rains could trigger mudslides and flooding.
Cathay Pacific Airways Ltd. said it expected flight operations to and from Hong Kong to be normal Friday, but anticipated delays on Sunday and Monday.
Friday, the typhoon moved past the northern tip of the Philippines where some residents of coastal villages were evacuated, The Wall street Journal reported.
By Sunday, the Hong Kong Observatory said on its website, weather conditions for Hong Kong and surrounding areas "will deteriorate significantly with high winds and rough seas."
"Usagi is a mature tropical cyclone and may become the strongest storm affecting Hong Kong so far this year," the observatory said.
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