In some provinces, authorities are predicting levels to rise to at least 40C and the national government has warned that forest fires could occur.

Mercury levels will start spiking on Saturday - "Big Heat" day in the traditional Chinese calendar.

In Zhejiang, in the south-east, some cities are issuing red alerts, the highest warning.

The province normally experiences temperatures in the high 20s in July but this year local authorities are warning of 40C in the next 24 hours.

To deal with the hot spells many in China turn to air conditioning in their homes, offices and factories however it could cause trouble for the national power grid.

Demand could reach a new high over the summer and the Ministry of Emergency Management has warned that safe operations would face "severe tests".

In July, Shanghai's temperature hit a sweltering 40.9C, equalling its hottest day since records began in 1873, hitting this mark the first time in 2017, Reuters news agency reports.

The city had to issue its third extreme heart warning of the summer.

Heatwaves have become more frequent globally, more intense, and last longer because of human-induced climate change.

The world has already warmed by about 1.1C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.