CHONGQING (AFP) - In chaotic and crowded subways, middle-aged and older residents of Chinese megacity Chongqing are taking shelter from the country's hottest summer on record - the air conditioning and subterranean cool providing respite from the scorching temperatures outside.

Multiple Chinese provinces are sweltering under a heatwave, prompting power curbs that have forced factories to close and lights to dim on some of the country's best-known city streets.

Experts have said the intensity, scope and duration of the heatwave could make it one of the most severe recorded in global history.

In Chongqing, home to 30 million, the Jialing River - a tributary of the Yangtze - is running dry and patience is wearing thin.

The Yangtze River at 6,300km is Asia's longest.

Desperate to escape the heat, hundreds of middle-aged and older residents have headed to the depths of the city's subway stations, whiling away the hours smoking, playing cards and napping.

Spread out snoozing in massage chairs or on blankets, some are street cleaners on their breaks, others manual labourers, while some just live close by or are out-of-work with nothing better to do.

Despite a recent Covid-19 outbreak in the city that saw 10 million summoned for mandatory testing, masks are few and between.

In a nearby supermarket that has become a hive of activity, one manager told AFP that many passing time underground have air conditioning at home but are bored and want to have a bit of subterranean fun with friends.

Nonplussed commuters squeeze past the crowds - a reminder that business in the city carries on despite the heat searing the streets above.