BEIJING- Light to moderate smog will blanket parts of northern, central and southwestern China from Sunday to Wednesday, the top observatory said on Sunday (Jan 14).
Affected regions include Chongqing municipality and provinces of Anhui, Hebei, Henan, Shanxi, Shaanxi and Sichuan, said the National Meteorological Center.
Some areas may be hit by heavy smog, the centre said, reported Xinhua news agency.
The authority added that smog in Sichuan and Chongqing will abate or even disappear from Monday (Jan 15) night under the influences of cold air and rain.
Local authorities in Sichuan and Chongqing on Sunday issued alerts for foggy weather, warning airports, freeways and ports to reinforce management to ensure safety.
The city of Shijiazhuang, the provincial capital of Hebei province, is expected to raise the alert for air pollution to the highest level on Sunday (Jan 14).
Hebei, the country's industrial heartland, is home to several of China's top 10 most polluted cities.
Local environmental authorities forecast heavy pollution would persist until Jan 17 in Shijiazhuang, which has always been badly hit by the winter smog.
Industrial enterprises in the city have been ordered to halt or reduce production, according to Xinhua. An odd-even vehicle number plate rule will be imposed in some areas to cut road emissions.
The year's first round of winter smog began blanketing much of China's northern region on Friday and is forecast to last for a week, environmental officials said.
Thirty-one cities including Beijing and Tianjin issued an orange alert, the second highest, on Friday.
The cities of Shijiazhuang, Tianjin, Linfen in Shanxi, Dezhou in Shandong and Zhengzhou in Henan are expected to see smog worsening on Tuesday. It will ease a little on Wednesday, worsen again on Thursday, and finally start to dissipate when a cold front arrives on Jan 18.
China has a four-tier warning system for severe weather, with red being the most serious, followed by orange, yellow and blue.
Under the orange alert, restrictions including limits on the production of heavily poluting factories as well as the use of vehicles are put in place.
To ensure implementation, the Ministry of Environmental Protection will despatch over 100 inspection teams to visit the 28 major regional cities to conduct field checks.