As a heat wave has swept across southern China in recent days, many people in big cities have found that air raid shelters are an ideal place to hide from the scorching sun.

These underground havens remain at temperatures of about 24-26 C, even when it exceeds 40 C outside. As a result, some cities have turned these shelters into rest centers which are open to the public for free in the summer, especially in China's "three stoves" of Nanjing, Chongqing and Wuhan, which have high summer temperatures.

Luo Ning, 65, a retiree in Nanjing, capital of Jiangsu province, has taken his 8-year-old granddaughter to a shelter near his home after lunch in recent days, where people can get something to drink, watch television, read magazines and books, use Wi-Fi and even access first-aid services.

"We feel more comfortable in this naturally cool place than in air-conditioned rooms," he said. "The shelters are well equipped with good ventilation and lighting, so we really enjoy staying here."

Nanjing Civil Air Defense Office stepped up its anti-infection measures amid the COVID-19 pandemic when it opened the city's shelters to the public this year, according to Yao Feng, an official from the office.

Everyone who wants to enter the shelters must follow infection prevention protocols and wear a mask all the time within them, she said. "Elderly people, children, travelers and sanitation workers are regulars in the shelters," she added.

In other cities, the interiors of shelters have been upgraded, which means they are able to provide better services, and Chongqing in southwestern China is a good example of this.

Chongqing had built hundreds of air raid shelters to protect civilians from Japanese warplanes which indiscriminately bombed the city from February 1938 to December 1944.

Those shelters are cool in the summer and warm in the winter, so local people have turned them into various kinds of places for daily use, such as restaurants, tea houses and wine cellars.

Residents of Chongqing have experienced unusually hot weather since the city issued its first red alert for summer heat on Monday. Temperatures as high as 42 C are forecast to continue in several parts of the city until the weekend, making such facilities even more popular.

A newly opened art gallery in a former air raid shelter now offers unique experience for locals while hiding from the heat.

The Stone House Art Space, 3.2 meters wide and about 60 meters long, can accommodate 70 people. Run by four artists, the roof and the walls of the shelter are decorated with paintings in the style of the Dutch impressionist Vincent van Gogh. A railway carriage-themed bar and a mini garden have also been built in the shelter.

"It is open to the public for free and we welcome everyone to take a break in our place," said Chen Huanwen, one of the founders of the art space. "We hope people can enjoy some art here too."