The government said more than 1.4 million people living near riverbanks and in low-lying areas have had to be evacuated, the official China Daily said on Saturday.
Zhang Zhitong, deputy director of the Office of State Flood Control and Drought Relief Headquarters, said the Pearl river, China's second largest waterway which crosses the south, breached warning marks on Thursday.
The government says 5.65 million people have been affected by heavy rains and mudslides in 172 cities in the provinces of Fujian, Jiangxi, Hunan, Guangdong, Sichuan and Guizhou, as well as the Guangxi Zhuang Autonomous Region.
Al Jazeera's Harry Fawcett, reporting from Nanping in Fujian, said the devastation was widespread in the country's key economic region, with the government estimating damage at $950m.
The rains and ensuing floods and landslides have engulfed roughly 300,000 hectares of crops and either destroyed or damaged about 98,000 homes.
Hui Liangyu, China's vice-premier, on Friday urged local governments to strengthen flood control efforts and try all means to save people endangered by the disaster.