Government monitors are calling the pollution hazardous, saying this is the worst it has ever been in China.
Residents say there's an acrid burnt smell. Some highways are closed and flights have been cancelled.
The pollution is blamed on China's rapid industrial growth and a rise in car ownership with no environmental standards.
The air pollution index in Beijing is at 755 and anything over a scale of 300 is considered an emergency. By comparison, the scale in the U.S. doesn't even go over 500.