An unprecedented July heat wave is sweeping China, with temperatures in many parts of the country exceeding 35 C and shattering past records for the month.

An arc of sweltering heat, stretching from the densely populated city of Chongqing in the southwest to the financial hub of Shanghai in the east, has in recent days enveloped a vast area that is home to nearly half of the nation's population.

On Tuesday, 16 provincial capitals and municipalities recorded temperatures above 35 C, while 29 national meteorological observation stations in Shaanxi, Shanxi, Hubei, Sichuan and Qinghai provinces broke their July records, according to a report released by weather.com, a website affiliated with the China Meteorological Administration.

Central and northwestern provinces such as Henan and Shaanxi are enduring scorching temperatures for up to 12 hours each day, leading to stifling mornings and oppressive nights, the website reported on Wednesday.

Xi'an, the capital of Shaanxi, and Luohe, a city in Henan, respectively recorded unprecedented nighttime temperatures of 32.6 C and 31.9 C on Tuesday, the website said. Most parts of southern China are recording nighttime temperatures above 24 C, with high humidity levels adding to the discomfort, it added.

Amid scorching temperatures, the quest for a cool night's rest has become a national obsession. The demand for home appliances, such as air coolers and air conditioners, is soaring in the landlocked central provinces of Hubei and Hunan, according to the report.

The heat spell hasn't spared traditionally cooler areas in northeastern China. Provinces such as Heilongjiang and Jilin, where the need for air conditioning was once rare, have witnessed a significant spike in air conditioner sales.

Data from All View Cloud, a Beijing-based company that monitors retail sales of household appliances, shows that offline sales for air conditioners in Heilongjiang surged nearly 818 percent year-on-year between June 23 and 30.

Most households in northeastern China did not have air conditioning until now, because they don't need it in summer, when nighttime temperatures generally stay below 20 C. However, on July 11, the nighttime temperature recorded in Harbin, the capital of Heilongjiang, was 25.4 C, a rare occurrence in the city's weather observation history, the website said.

The frequency of extreme heat conditions this summer is likely to increase, weather experts warned.

Sun Qianqian, a meteorologist at Weather.com, said a subtropical high-pressure system, which causes warm and usually dry weather, is expected to strengthen and expand over land on Friday.

Some provinces such as Qinghai, Sichuan and Shaanxi are expected to experience "exceptionally rare extreme heat", she added.

lihongyang@chinadaily.com.cn