Authorities in the Chinese capital have warned of "severe pollution" and advised the city's 20 million inhabitants to stay indoors.
Beijing has been shrouded in grey smog since Friday, reducing visibility to a few hundred metres.
Some pollution readings in the city have reached 22 times the level considered safe by the World Health Organization - despite commitments from the government to improve the environment.
Beijing and many other northern cities in China are notorious for their winter smog, which is caused by a combination of air pollution and weather conditions.
More than a quarter of a million people in China's biggest cities could have their lives cut short by high levels of air pollution, according to a recent joint study by Peking University and Greenpeace.
The Ministry of Environmental Protection has forecast severe pollution for Beijing and other areas until Tuesday, when strong winds are expected to clear some pollutants.