Southern China is set to be hit by its second typhoon inside a week.
Typhoon Chanthu was upgraded from a tropical storm on Wednesday after gathering strength over the South China sea.
Officials say downpours could worsen already-flooded areas and trigger landslides.
Five provinces are expected to be hit including Guangdong and the island of Hainan.
Flooding in China, the country’s worst for a decade, has killed more than 700 people this year, while 347 are still missing.
Fears have been raised of a repeat of the 1998 Yangtze river floods in which 4,000 died.
But Chinese Premier Wen Jiabao insists his government is well-prepared to avert another mass disaster of that scale.