Temperatures topping 40 degrees Celsius have broiled the southwest city of Chongqing, pushing some locals to use innovative ways to cope with the increasingly hot weather.

"It's getting hotter and hotter," said Liu Fengying, 60, a local resident. As afternoon temperatures soared on Thursday, Liu avoided the heat by playing card games and sharing snacks with friends among around 100 retirees sheltering in the air-conditioned chill of a subway entrance.

Xie, 79, one of dozens of swimmers who gathered at a tributary of the Yangtze River as the sun started to set on Thursday, cools down with regular swims in China's longest river.

And on the same night, Qiu Xianhui, 36, came with friends to eat hotpot at a restaurant in one of the city's old bomb shelters, where the air cools naturally.

Record heat across China has strained its power grid as demand surges to new all-time highs, now in excess of 1.5 billion kilowatts, with records broken four times just in July.

After daily peaks exceeding 40 degrees Celsius for a week, Chongqing elevated its heatwave warning to the highest level – a red alert – on Thursday, with 21 out of its 38 districts forecast to hit up to 43 degrees Celsius. A peak of 44 degrees Celsius is projected for Sunday.

Historically, daily peaks in the city of nearly 32 million people have rarely exceeded 39 degrees Celsius in July, which is already very hot by global standards. (Reuters)