China's weather agency said areas of Jiangxi, Anhui, Hunan, Hubei, Guizhou, Guangxi, Guangdong and Hainan faced a high risk of rain-related disasters, including landslides, flash floods and severe urban flooding and waterlogging.
Authorities said they have allocated 150 million yuan ($A31 million) for disaster relief and launched emergency responses in several affected areas.
Many residents in Jingzhou, a city in central Hubei, were knee-deep in water and able to catch fish swimming in the streets, according to images posted on Chinese video platform Douyin.
Some cars were nearly completely submerged on roads surrounded by residential and commercial buildings.
Ten people were confirmed dead after a truck carrying 15 farm workers fell into a flooded river in China's southwestern region of Guangxi amid heavy rain, state broadcaster CCTV reported.
In separate incidents, heavy rain and flooding killed four people in southwestern Guizhou province, three in a low-lying village in central Hubei province, and another person in southern Hunan province, CCTV said.
Schools, businesses and transport services have been suspended, and authorities are relocating residents in some parts of Hubei and Hunan, state media reported.
The unusually large area of intense rainfall - spanning more than 1000km - was due to the convergence of abundant moisture from the Bay of Bengal, the South China Sea and the Pacific Ocean.
The slow-moving nature of the weather system also led to the high cumulative rainfall, according to Chinese meteorologists.
China's National Meteorological Centre said severe weather would gradually move east and south across China during the next two days.
From Wednesday, the heaviest rainfall is expected along the middle and lower reaches of the Yangtze River.
China's southern Hainan island issued a geological disaster warning on Tuesday, as a mountainside collapsed onto a highway in Lingshui, prompting authorities to close several major roads in that area of the island.
Separately, authorities in Guangxi set up temporary shelters on 99 sites for more than 4000 residents and relocated 7000 people after a magnitude 5.2 earthquake on Monday, which sent tremors across multiple cities in the region.
