BEIJING, Feb. 23 (Xinhua) -- China is taking measures to control air pollution, including limiting vehicles on the road and suspending factory production, as smog persisted in many areas for the fourth consecutive day.

North China's Shijiazhuang, capital of Hebei Province, went on orange alert for smog, the second highest, early Sunday morning, and an emergency response initiated.

The emergency response cuts private vehicles in use by 20 percent based on the last digit of the license plate. Vehicles with last plate digit of 1 or 6 must be off the road in urban areas on Sunday.

Beijing went on orange alert on Friday for the first time. Manufacturing plants in the city have suspended or cut production, building work is halted, and no barbecues are allowed.

Physical education classes, outdoor exercise and sports meets at kindergartens, primary and high schools have been called off.

According to the Ministry of Environmental Protection, almost all of north, east and central China are suffering. Beijing and provinces of Hebei, Shanxi, Shandong, Henan and Liaoning reported severe smog.

In respond to the pollution, the Ministry said on Sunday said that it has sent 12 inspection teams to Beijing, Tianjin, Hebei and their surrounding areas to check the response to the pollution.

China's meteorological disaster alerts are categorized as blue, yellow, orange and red in order of increasing severity.