A red alert indicates the most serious air pollution (AQI above 300) for three consecutive days. An orange alert indicates heavy to serious air pollution (AQI between 200 and 300) alternately for three consecutive days. A yellow alert indicates severe pollution for one day or heavy pollution for three consecutive days.

A red alert requires traffic to be cut with alternate driving days for even- and odd-numbered license plates, and schools to be suspended. Industrial plants are closed or told to reduce production when an orange alert is issued.

Despite a spate of control measures, Beijing and neighboring cities, mainly in Hebei Province, are prone to frequent air pollution.

The current smog, which started on Thursday, is also forecast to persist in other northern regions, including Tianjin, Hebei, and parts of Shandong, Shanxi, Shaanxi, Henan and Liaoning for the next three days, according to the China Meteorological Administration.

A cold front is forecast to ease or disperse the smog on Thursday, said the administration.

While the cold front is days away, regions are rolling out emergency measures to battle air pollution, which is increasingly a source of complaints and frustration among urban residents.

Authorities in Shanxi have ordered outdated production facilities to suspend production to improve pollutant treatment. Hebei dismantled some high-polluting steel mills Sunday to reduce annual capacity by 6.7 million tonnes, part of its efforts to cut steel capacity by 60 million tonnes between 2013 and 2017.

Authorities in Shijiazhuang, capital of Hebei, ordered the removal of one-fifth of vehicles from roads based on the last digit of the license plate starting Sunday. A similar measure went into effect in Tianjin on Sunday.

To help tackle pollution in the long term, the municipal government in Tianjin went further to launch a clean energy initiative on Monday, saying it will promote the use of 12,000 new energy vehicles mainly in the public transport and logistics sectors.