At least 15 people have been killed by floods in southwestern China as seasonal torrents hit mountain areas, authorities said Wednesday.

Another four people were reported missing by mid-morning in Chongqing, a vast mountainous region of 31 million, almost all of which has now been designated as having flood risk, according to the local government website.

The Chongqing floods appear to be China's deadliest amid deluges in other parts of the country. Tens of thousands of people have been evacuated. In just one southwestern province, Sichuan, more than 85,000 people have been evacuated due to flooding, the official Xinhua News Agency reported.

Chongqing’s flood warning has been upgraded from level four to level three, reflecting the growing seriousness of the crisis.

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Rescue teams in inflatable boats were ferrying villagers to safety and workers were clearing roads blocked by landslides, according to photos posted on the government website.

Seasonal flooding hits large parts of China every year, particularly in the semi-tropical south. However, some northern regions this year have reported the worst floods in 50 years.

In 2021, more than 300 people died in the central province of Henan. Record rainfall inundated the provincial capital of Zhengzhou on July 20 that year, turning streets into rushing rivers and flooding at least part of a subway line.

China’s deadliest and most destructive floods in recent history were in 1998, when 4,150 people died, most of them along the Yangtze River.

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Meanwhile, much of China, including Beijing, is sweltering under heatwaves that arrived earlier and have lasted for more consecutive days than in decades. Temperatures in the capital were forecast to hit 40 degrees Celsius (104 Fahrenheit) on Thursday.