A tributary of the Yangtze River, the longest river in Asia, has shrunk as a severe heatwave beat down on southwest China.

Footage shows the Jialing river along Chongqing reduced to puddles, with the dried-up riverbed left exposed due to the drought on August 16.

The sweltering heat and lack of rain has affected the supply of drinking water, hydropower, and irrigation, local media reported. Authorities said fire trucks have had to deliver water to two outlying villages in Chongqing.

State media outlet Xinhua said the Chinese national observatory has raised a red alert - the most severe warning - for high temperatures as heatwaves of up to 40 degrees Celsius scorched parts of the country on Wednesday.