Over the next 10 days, China will face the return of new waves of heat from east to west, Reuters reported.

Authorities in several coastal cities are already issuing warnings of the highest levels of heat, and warning of the risks of dam breaks as glaciers melt faster.

Temperatures are expected to spike on Saturday and develop into heat waves, defined as periods of atypically hot weather for three or more days. The coming Saturday is the day of the "big heat wave" in China's lunar calendar almanac.

The heatwave period is expected to be similar to the July 5 to 17 heat waves, but more regions could be affected by temperatures of 40 degrees Celsius or higher, said the chief forecaster at the National Meteorological Center.

Some cities in Zhejiang province, home to many factories and exporters, declared a red danger level Friday, the highest in a three-level warning system, predicting temperatures of at least 40 degrees Celsius in the next 24 hours.

The strain on the national power grid could reach a new high this summer as demand for air conditioning in homes, offices and factories rises sharply, the Ministry of Emergency Situations warned Friday.

"For all the plants in China and in Shanghai, we have rules to follow," said Leo Zhang, president of chemical manufacturer Sika China. "Every year we do things to make the work more comfortable, for example giving workers ice-creams when it gets too hot."

Zhejiang, as well as parts of Fujian, Guangdong, Hunan, Jiangxi and the city of Chongqing, also stand at risk of forest fires in the near term, the ministry said.

In the western region of Xinjiang, accelerated glacial melt through July 29 poses risks to rivers and dams, the China Meteorological Administration said on Friday, warning particularly of a high risk of dam failure on a tributary of the Aksu River near China's border with Kyrgyzstan.

Scientists warn that climate change will cause heat waves to become more extreme and hot and frequent.

According to Chinese media, the hottest period in the last 300 years was in July 1743 during the Qing dynasty, with a French missionary in Beijing said to have recorded an all-time high of 44.4C.

According to the China Meteorological Administration, temperatures in the oasis city of Turpan could reach 50°C next week.