Chinese cities are limiting the number of cars on roads and have temporarily shut down factories to cut down pollution during a national “red alert” for smog.

State media reported Monday that more than 700 companies stopped production in Beijing, and that traffic police were restricting drivers by monitoring their license plate numbers.

Dozens of cities closed schools and took other emergency measures after a “red alert” was issued from Friday night to Wednesday for much of northern China.

Authorities in northern Hebei province ordered coal and cement plants to temporarily shut down or reduce production.

People told to stay indoors as air pollution in Beijing reaches hazardous levels Show all 5 1 /5 People told to stay indoors as air pollution in Beijing reaches hazardous levels People told to stay indoors as air pollution in Beijing reaches hazardous levels beijing-1.jpg A woman wearing a mask crosses a road during severe pollution in Beijing GETTY People told to stay indoors as air pollution in Beijing reaches hazardous levels beijing-2.jpg A woman wearing a mask walks on a street during severe pollution in Beijing GETTY People told to stay indoors as air pollution in Beijing reaches hazardous levels beijing-3.jpg Parking attendants stand on a roadside during severe pollution in Beijing GETTY People told to stay indoors as air pollution in Beijing reaches hazardous levels beijing-4.jpg Traffic makes its way through Beijing GETTY People told to stay indoors as air pollution in Beijing reaches hazardous levels beijing-5.jpg Severe pollution clouds the Beijing skyline GETTY

Elsewhere, hospitals prepared teams of doctors to handle an expected surge in cases of pollution-related illnesses.

China's long-standing air pollution is blamed on its reliance on coal and emissions from older cars.