Some power plants and chemical producers in the region had not scaled back operations in line with regulations, and drivers in Beijing had also been ignoring traffic restrictions, according to China Environmental News, the official publication of the Ministry of Environmental Protection.
The paper said as many as 24 cities in northern China had issued pollution "red alerts" by Tuesday but, despite the implementation of emergency measures, smog concentrations had continued to increase in parts of the region.
That included several major cities in the industrial province of Hebei, which surrounds Beijing.
Red alerts are issued when the Air Quality Index (AQI) is forecast to exceed 200 for more than four days in succession, 300 for more than two days or 500 for at least 24 hours.
In Handan, a major steel producer, the 24-hour average AQI at one monitoring station reached a record 780, according to environmental group Greenpeace.
Large hospitals in the port city of Tianjin, less than 100 miles southeast of Beijing, saw a surge in asthma and other respiratory issues, China's People’s Daily reported. The pollution forced the city to close the highways and caused delays and cancellations for dozens of flights, Xinhua said.
Off-the-charts air pollution chokes many places in #Hebei province, w/ PM2.5 levels exceeding 1,000 in its capital city of #Shijiazhuang," the People's Daily tweeted. Some coal and other industrial plants in Hebei were ordered to shut down until the smog eases.
Beijing's meteorological authority told Agence France-Presse the worst haze would hit the city Monday night and linger until Tuesday. Under a contingency plan for severe air pollution, the city shut down more than 700 heavy industry plants and required 500 more to reduce production, the South China Morning Post reported
Beijing Capital International Airport said on its microblog that 181 flights had been cancelled, although 50 were able to operate.
Flights had already been affected at other airports, including in the neighbouring city of Tianjin.
The airport officially blamed fog but PM 2.5 levels soared to more than 450 micrograms per cubic metre in parts of the city overnight, according to the Beijing Government.