China on Tuesday issued its highest-level red rainstorm warning for parts of Guangdong, a local weather agency said, as the southern province was battered by downpours.

The megacity of Shenzhen was among the areas listed as experiencing "heavy to very heavy downpours", the city's meteorological observatory said, adding the risk of flash floods was "very high".

Torrential rains have lashed the vast southern province of Guangdong in recent days, swelling rivers and raising fears of severe flooding that state media said could be of the sort only "seen around once a century".

State news agency Xinhua said 110,000 Guangdong residents had been relocated since the downpours started over the weekend.

Four people died and 10 were missing, Xinhua reported.

China is no stranger to extreme weather but in recent years has been hit by severe floods, grinding droughts and record heat.

Climate change driven by human-emitted greenhouse gases makes extreme weather events more frequent and intense, and China is the world's biggest emitter.