CITIES in northern China took emergency action yesterday to combat choking smog, limiting the number of cars allowed on the roads and temporarily closing factories.

More than 700 companies halted production in Beijing and traffic police restricted drivers by monitoring their licence plate numbers.

Dozens of cities ordered schools to shut and took other emergency measures after a “red alert” was issued for much of northern China, lasting until tomorrow.

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

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.

“If you are tracking back to the first day of this episode, you can see that the layer of the smog is moving slowly from the south to the urban area in Beijing and then to the north,” said Greenpeace climate campaigner Dong Liansai in Beijing.

“You can easily find a large concentration in the regions south of Beijing.”

Mr Dong said that emissions from factories in nearby provinces were the main cause of the smog choking the capital.

The smog had earlier grounded flights in some cities and closed motorways due to low visibility.