According to the National Meteorological Center, thick smog shrouded Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan, Shaanxi and Jiangsu on Wednesday.

The sky is expected to clear to blue on Thursday with a cold snap blowing the haze away on Wednesday evening, the National Meteorological Center said on Wednesday.

Temperatures in central and eastern China will see dramatic drops of up to 10 degrees Celsius before Friday, according to the NMC’s weather forecast.

The choking smog shut down highways and forced schools to suspend outdoor activities in parts of the region since Sunday.

In Shandong and Hebei, some primary schools suspended outdoor activities for health reasons.

"All sports and exercises were taken indoors because of the heavy pollution," Xu Shuhai, vice-president of No 8 Middle School in Hengshui, Hebei province, told Xinhua News Agency on Wednesday.

Research published in the Proceedings of the National Academy of Sciences, a US multidisciplinary scientific magazine, in July, said that air pollution from burning coal caused people in northern China to live an average of 5.5 years less than those living in the south. Coal has been used to provide heat to the north for decades.

"The study gives a clear answer to the link between life expectancy and air pollution," Li Hongbin said in an earlier interview with China Daily. Li is an economics professor at Tsinghua University School of Economics and Management in Beijing who collaborated with researchers in China, the US and Israel on the study.

A monitoring network would be established in 16 provinces to study the influence of air pollution on health, over the next five years, health authorities said.