The air pollution emergency management headquarters said that a total of 40 cities in north China, including Beijing and Tianjin, have issued alerts for air pollution. Baoding, Handan, Langfang and Xingtai in the neighbouring Hebei province have also issued red alerts.
Beijing was hit with severe air pollution on Tuesday, with pollution levels expecting to reach grade six on a six-grade pollution gauging system, according to Beijing Municipal Environmental Monitoring Centre (BMEMC).
"Affected by increased humidity and temperature inversion, the density of PM2.5 (particles smaller than 2.5 micrometers used to measure air quality) may exceed 500 micrograms per cubic metre on Tuesday," according to Li Yunting, an environmental expert from BMEMC.
China's port city of Tianjin and other 12 cities from provinces of Hebei, Henan and Shandong have issued orange alerts. Yellow alerts and blue alerts have been issued in 17 cities and five cities respectively, according to the air pollution emergency management headquarters of Beijing.
China has a four-tier colour-coded weather warning system, with red representing the most severe weather, followed by orange, yellow and blue. Tianjin will upgrade its orange alert to red from 0.00 a.m. on Wednesday to 6.00 a.m. Thursday, according to a government statement.
During the red alert, cars will be allowed on the roads depending on whether their license plate ends in an odd or even number. Enterprises and public institutions will adopt flexible working hours and large outdoor activities and construction work will be suspended.
Kindergartens, middle schools and primary schools will also cancel classes on Wednesday. Key polluting industries will cut production as continuous cleaning operations were conducted in the city's downtown areas.
Heavy smog has hit the country's Beijing-Tianjin-Hebei region on three occasions since late November. Low wind speed, high humidity and unfavourable wind conditions were the main causes of the smog, according to Li.