Southern China is expected to see torrential rains until Tuesday, state media reported on Friday, with no immediate reprieve to the region inundated by downpours in the past week.
Authorities had issued warnings of "extreme weather events" as early as April, ahead of the rainy season that signals the seasonal transition from spring to summer in June.
China is historically prone to floods, triggering landslides and swamping many acres of farmland.
In recent times, the country has grown even more vulnerable, owing to deforestation, the reclamation of wetlands and the storage of water for power generation and irrigation.
China also blames climate change for the increase in extreme weather events.
"Weather conditions in China will tend to be unfavourable this summer," an official at the country's aviation regulator said at a news briefing on Friday, adding that severe convective weather can be expected.
Late on Thursday, a tornado ripped through parts of Guangzhou during a heavy rainstorm, local media reported, cutting off power supply to over 5,400 users in the sprawling southern city, capital of Guangdong province.
Media in Guangzhou reported dangerous water levels with high waves in the broader Pearl River Basin, prompting the central government to dispatch flood prevention workers.
Since May, precipitation in the Pearl River Basin - a vast river system encompassing Guangdong and parts of Guangxi, Jiangxi, Hunan, Guizhou and Yunnan - has risen to its highest since 1961, according to state media on Friday, citing China's National Climate Center.
In Fujian province north of the basin, authorities warned that recent record-breaking rainfall would persist into next week, posing a high risk of natural disasters.
Meanwhile, temperatures in central and northern China are expected to hit unusual highs into next week, surpassing 40 degrees Celsius (104 degrees Fahrenheit).
The abnormally warm weather has already enveloped the Henan capital of Zhengzhou, which was hit by record rainfall and paralysed by devastating floods last summer.
(Reporting by Ryan Woo in Beijing and Beijing newsroom; Writing and additional reporting by Liz Lee in Kuala Lumpur and Stella Qiu in Beijing; Editing by Michael Perry and Kim Coghill)