Ji'nan, capital of east China's Shangdong Province, is shrouded with smog on Oct. 20, 2015. (Photo: Xinhua/Zhu Zheng)
Smog has covered large parts of north China, and the public has been warned to take precautions.
Parts of Shandong, Henan, Shaanxi and Jiangsu provinces will be affected by smog until Saturday, the National Meteorological Center (NMC) forecast.
Xi'an, capital of northwest China's Shaanxi Province, on Tuesday activated an air pollution emergency response, banning excavation at more than 60 percent of the city's construction sites.
At least 13 cities in Shandong Province have been hit by smog since Friday, the provincial meteorological station said.
The NMC issued a yellow alert and advised children, the elderly and people with respiratory diseases to stay indoors.
China has a four-tier color-coded weather warning system, with red representing the most severe weather, followed by orange, yellow and blue.
A cold front will hit north China starting Sunday and is expected to disperse the smog, according to the NMC.
