Calling the situation "grim", local weather officials said sections of rivers and tributaries at the Xijiang and Beijiang river basins are hitting water levels in a rare spike that only has a one-in-50 chance of happening in any given year, state broadcaster CCTV news said on Sunday.
China's water resource ministry issued an emergency advisory, CCTV reported.
Guangdong officials urged departments in all localities and municipalities to begin emergency planning to avert natural disasters and promptly disperse disaster relief funds and materials to ensure affected people have food, clothing, water and somewhere to stay.
The province, a major exporter and one of China's main commercial and trading centres, has seen major downpours and strong winds for several days, in a weather pattern which has also affected other parts of China.
A 12-hour spell of heavy rain, starting from 8 p.m. (1200 GMT) Saturday, battered the central and northern parts of the province including the cities of Zhaoqing, Shaoguan, Qingyuan and Jiangmen where rescue workers have been dispatched.
More than 45,000 people have been evacuated from Qingyuan, according to state media, and some power facilities in Zhaoqing were damaged, cutting power to some places.
Overall in Guangdong, 1.16 million households lost power due to the heavy rains, according to state-backed media.
About 1,103 schools in Zhaoqing, Shaoguan and Qingyuan will suspend classes on Monday, Chinese state radio said.
WATER TOWN
"Please look at Zhaoqing's Huaiji County, which has become a water town. The elderly and children in the countryside don't know what to do with power outages and no signal," said one user on the popular social media site Weibo.
Raging floodwaters swept one vehicle down a narrow street in Zhaoqing, a video released by Hongxing News showed.
"It rained like a waterfall for an hour and a half on the highway driving home last night," said another Weibo user. "I couldn't see the road at all."
Authorities in Qingyuan and Shaoguan also suspended ships from travelling through several rivers, with maritime departments dispatching forces to be on duty and coordinate emergency tugboats and emergency rescue vessels.
Many hydrological stations in the province are exceeding water levels, weather officials warned, and in the provincial capital Guangzhou, a city of 18 million, reservoirs have reached flood limits, city officials announced on Sunday.
Data showed 2,609 hydrological stations with daily rainfall greater than 50 mm (1.97 inches), accounting for about 59% of all observation stations. At 8 a.m. Sunday, 27 hydrological stations in Guangdong were on alert.
In neighbouring Guangxi, west of Guangdong, violent hurricane-like winds whipped the region, destroying buildings state media video footage showed. Some places have also experienced hailstones and major flooding, CCTV said.
In another video, rescuers could be seen trying to save an elderly person clinging to a tree half-submerged in flood waters.
As of 10:00 a.m. (0200 GMT), 65 landslides were recorded in the city of Hezhou located in Guangxi, state media reported.
Weather forecasters are expecting heavy rain through Monday in the Guangxi region, Guangdong, Fujian and Zhejiang provinces.
Reuters