China entered its flood season on Monday, 11 days earlier than usual, the State Flood Control and Drought Relief Headquarters said.
Heavy rains have hit parts of south China since Saturday, pushing water levels in some rivers well above warning lines, the headquarters said.
Strong rain will continue to pelt south China in the coming 24 hours, the National Meteorological Center (NMC) forecast, while asking relevant departments to strengthen disaster prevention.
Parts of Guangdong, Hunan, Jiangxi and Guizhou provinces will be hit by rain or storms, with maximum rainfall reaching up to 50 millimeters per hour, the NMC said in a statement on its website.
The NMC issued a blue alert for rainstorms in southern regions on Monday night, warning that people be alert for possible risks including mud-rock flows and landslides.
China has a four-tier warning system for severe weather, with red being the most serious, followed by orange, yellow and blue.