Flooding has also been reported in Jiangxi province and Guangxi, a major sugar-producing region neighboring Guangdong.
Analysts said the floods' impact on industrial and agricultural production would be limited.
"China has floods every year and droughts are a much more serious problem for China's food supply and food prices," Ting Lu, China economist at Merrill Lynch in Hong Kong said.
But heavy rain likely in the next few days would "increase the destructiveness of flood hazards and make the flood prevention and relief situation nationwide even more serious," Xinhua cited the Ministry of Civil Affairs as warning.
Adding to fears just months before the country hosts the Olympics, the national meteorological service said the 5,500-km (3,400-mile) Yellow River flowing through the north might also see "quite large" floods this year, Xinhua reported late on Sunday.
The Yellow River, China's second longest after the Yangtze, has experienced devastating floods in the past, but in recent decades has been more prone to water scarcity.
At a cabinet-level meeting on Monday, Chinese Premier Wen Jiabao ordered authorities to check renewed threats on dams strained by floodwaters in quake-hit areas in Sichuan and parts of neighboring provinces.
"Aftershocks have continued into the flooding season and rainfall has noticeably increased (Officials) must carry out further engineering measures to eradicate threats on dammed reservoirs where dangers remain," he said in notes on the meeting posted on the central government website (www.gov.cn).
Landslides in quake-hit regions have caused dozens of swelling "quake lakes" which officials fear could burst and threaten thousands of people in villages downstream. The walls of a number of existing dams were also weakened by the quake.
Authorities are struggling to evacuate tens of thousands of people from quake-hit areas under threat from rain-triggered landslides and to provide housing for millions of people left homeless.
With tremors still jolting hillsides, officials have decided to relocate 50,000 residents at risk of landslides in Wenchuan County, the epicenter of the quake.
Last week, county officials told threatened residents to move to safer areas, and troops had relocated 3,000 by Monday, Xinhua reported. All at risk must be moved by the end of June, before the rainy season starts in earnest, it said.
The flooding and foul weather is the latest in a string of disasters to befall China this year. Many of the same provinces were paralyzed by freak cold weather in January and February.
