Pollution may make economy stumble (2)

The factories ordered to halt operations include two cement plants, and others involved in chemicals, metallurgy and building materials, he said.

Up to 30 percent of government vehicles have also been banned from the capital's roads on heavily polluted days, according to a spokesman for the Beijing Traffic Management Bureau.

Drivers found guilty of breaking the rules face penalties, but the spokesman did not elaborate.

Air quality dropped dramatically on Thursday and steadily worsened over the weekend, said Zhang Dawei, who heads the city's environmental protection monitoring center.

By Saturday, official data showed the density of PM2.5 — particles of 2.5 microns or smaller that can damage the lungs — had reached 900 micrograms per cubic meter in several Beijing districts.

It was the highest level recorded since authorities began releasing the data to the public in early 2012.

The safe daily level is 25 micrograms per cubic meter, according to the World Health Organization.

Coal emissions and vehicle exhaust fumes played a major role in the pollution and a low-pressure weather front trapped the polluted air.

"Beijing is a huge city with a lot of heavy industry," Zhang said. "Under certain atmospheric conditions, the pollution is trapped.''

The China Climate Bulletin, released by the China Meteorological Administration on Monday, said hazy conditions primarily occurred in two periods; between January and March and October and December.