Beijing was put on yellow smog alert on Sunday, imposing restrictions on building and cooking outdoors.
The Air Quality Index in Beijing stood at between 200 and 300 out of 500 on Saturday and Sunday, meaning “very unhealthy”.
Forecasters said the pollution would continue on Monday and be dispersed by a cold snap on Tuesday. Smog had also affected Tianjin, Hebei and Shaanxi, the National Meteorological Centre said.
China has a four-tier system for air pollution, with red being the most serious, followed by orange, yellow and blue. Under the yellow warning, barbecues, work at construction sites and the burning of straw by farmers are not allowed.
Children, the elderly and people with respiratory or cardiovascular diseases are advised to stay indoors and people are advised to take public transport.
Environmental Protection Minister Chen Jining held an emergency meeting on Sunday to address the issue. Experts at the meeting said pollutants were concentrated because of weather conditions, Caixin reported.
Wang Zifa, a researcher at the Chinese Academy of Sciences, was quoted as saying that northern China would face more serious air pollution in autumn and winter this year.
He said the impact of El Nino and temperature inversions would make it difficult for pollutants to be dispersed.
The environmental ministry said on Thursday that air quality in the Beijing-Tianjin-Hebei region had improved in the first eight months of this year from the same time in 2015, but critics said more needed to be done to clean up the air.
Decades of economic development on the mainland has spawned massive pollution.
On Thursday, a Dutch inventor opened what he calls the world’s largest air purifier in Beijing. The seven-metre Smog Free Tower, part of a project started by artist and innovator Daan Roosegaarde, is said to capture 75 per cent of smog particles that have diameters of 2.5 microns and 10 microns, and release clean air around the structure.
Some Beijing residents said they would like to see more such towers to raise awareness of pollution in Beijing, but others questioned whether the effectiveness of the tower was backed by scientific research.