Scorching heat has persisted in northern and eastern parts of China since Monday, driving up the number of emergency calls and sending hundreds of people to hospital with heat-related illness.

Beijing, Shanghai and Chongqing as well as cities in Hebei, Henan, Shandong and Jiangxi provinces have issued heat wave warnings, with temperatures soaring to 40 C in many areas on Wednesday.

"The heat wave is expected to move toward the south, with rainfall coming around Friday in the north, cooling down the hot weather," said He Lifu, chief forecaster of the National Meteorological Center.