BEIJING - After days of lingering smog, the Beijing municipal government has for the first time issued an orange alert for heavy air pollution, initiating an emergency response.

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The alert, issued on Friday and the second highest after red, requires manufacturing plants in the city to suspend or cut production, building work to be halted, and even no barbecues, according to the emergency response program.

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

If the alert is raised to red, schools will be suspended and half of the number of vehicles will be off the road based on even- and odd-numbered license plates, according to the program.

Smog will continue to blanket China's north and central regions on Saturday as the the National Meteorological Center (NMC) issued a yellow alert for air pollution.

Beijing, Tianjin and parts of Hebei, Shandong, Henan, Shaanxi and Shanxi provinces expect heavy air pollution from Saturday morning to Sunday morning, according to the NMC forecast.

Beijing, Tianjin and Hebei Province have been suffering heavy smog since Thursday. On Friday, PM 2.5 readings in these regions kept rising and exceeded 200 micrograms per cubic meter, far above the 25 micrograms level considered safe by the World Health Organization.

The NMC on Thursday forecast the smog would last for a week as no cold front is in sight to help disperse it.