On Tuesday morning, a grey haze blanketed Shenyang - the capital city of Liaoning Province. The air quality index hit 224, which is classified as heavily polluted on China's six-level air quality indicator.

During this morning's rush hour in Shenyang, local residents have put on masks and outdoor sports activities for primary and middle schools were ordered to be halted throughout the day, doctors from Shengjing Hospital of China Medical University in Shenyang told CGTN that the number of patients with respiratory disease had jumped sharply in the past few days.

According to the national meteorological center, the thick haze could hang around until Thursday, when a fresh wave of cold air is expected to sweep across the fog-shrouded areas, weakening or dispersing the smog, as for now local authorities pointed out that visibility would be as low as 200 meters in the cities of Shenyang, Jinzhou and Dalian.

China's National Environment Monitoring Center said 27 Chinese cities, including Beijing, reached the heavy pollution level on Monday. Linfen in northern Shanxi Province, Weifang in eastern Shandong Province and Huludao in northeastern Liaoning Province reported the top three pollution readings. Experts suggest that local authorities should strengthen control of coal-fired power plants, gas-fueled vehicles and industrial emissions in the major polluted cities.