Typhoon Usagi has battered coastal communities in southern Taiwan and the northern Philippines and is now heading for Hong Kong and the coast of south China.
It has been downgraded slightly, but it still poses a significant threat to Hong Kong and China's manufacturing heartland in the Pearl River delta.
Meteorologists say the storm is the most powerful this year.
Taiwan deployed more than 1600 troops in "high risk" areas prone to flooding and landslides. The BBC reports another 24,000 were on standby.
Emergency services in the Philippines were on heightened alert.
State media in China report the State Oceanic Administration has issued a class one emergency warning.
Typhoons are common during the summer in parts of East Asia.