Dozens of Chinese cities baked in scorching temperatures as heatwaves melted the roofs of buildings and buckled roads and sweltering weather drove people to seek the cool in raid shelters underground.

Nearly 70 cities – including Shanghai and nearby Nanjing – have issued red alerts, the highest in a three-tier heatwave warning system, forecasting temperatures in excess of 40 degrees Celsius.

Shanghai warned its 25 million residents to prepare for hot weather this week. Since record-keeping began in 1873, Shanghai only had 15 days with temperatures above 40 degrees Celsius.

A widely shared photo on social media showed one Covid tester in a full-body hazmat suit hugging a one-metre tall block of ice by the road. At a sprawling Shanghai wildlife park, its staff had to go through eight tonnes of ice a day just to keep its animals cool.

China is facing a summer of contrasts this year, with heatwaves and heavy rainfall taking turns to wreak havoc across the country. Authorities, citing climate change, have warned of potential weather disasters from mid-July, traditionally the hottest and wettest time of the year.

The National Meteorological Centre has advised people to take necessary protective measures against the heatwave and avoid outdoor activities during high-temperature periods.

In a town in southern Jiangxi province, a section of a road arched up at least 15 centimetres due to the heat, state television showed.

Nanjing has opened up its underground air-raid shelters to residents since Sunday, with its war-time bunkers equipped with WiFi, books, water dispensers and even microwave ovens. The city issued a red alert on Tuesday.

In Chongqing, the roof of one of its museums literally melted, with the tiles of a traditional Chinese roof popping as the heat dissolved the underlying tar. The city raised a red alert on Monday. Chongqing has also deployed sanitation water-spraying trucks to keep its roads cool.

This week, high temperatures, humidity and ultra-violet radiation are also forecast to envelope the central city of Wuhan. (Xinhua/Reuters)