The city of Shenzhen has been lashed by the heaviest rain since records began there in 1952, state media reported on Friday.

"From 5pm Thursday to 6am Friday, the average rainfall in Shenzhen was 202.8 mm, and the maximum cumulative rainfall reached 469 mm," Xinhua reported, adding that the rainfall had broken multiple meteorological records since they began 71 years ago.

Xinhua said heavy rain was forecast to continue on Friday.

"Shenzhen's flood, drought and typhoon control headquarters issued a notice Friday morning that primary and secondary schools and kindergartens across the city will suspend classes on Friday in consideration of ensuring the citizen's safety and property," the news agency reported.

Services on parts of six subway lines were suspended and authorities warned people to stay away from "dangerous areas" such as mountains, rivers, slopes, and retaining walls.

Xinhua news agency also shared video of residents holding onto safety lines waded cautiously through knee-deep floodwaters late on Thursday in the metropolis of 17.7 million people.

Rescuers also cordoned off overflowing manholes, carried a child from a stranded vehicle and guided others to move their motorcycles through the murky waters, the videos showed.

Waters in Shenzhen reservoir reached their limit early on Friday, prompting authorities to begin discharging water and warning residents downstream in Futian and Luohu districts to keep away from rivers.

Authorities suspended services at Liantang Port and Wenjindu Port connecting Shenzhen and Hong Kong due to flood damage.

Fresh food supplies, passengers and trucks were diverted to other ports.

About 130km from Shenzhen, schools in 10 districts of Guangzhou city were suspended for the day or delayed their opening, while Zhuhai city warned of waterlogging in urban and rural areas, and potential landslides. (AFP/Reuters)