BEIJING, Jan. 13 (Xinhua) -- Smog will affect parts of northern China from Saturday to Wednesday.

Mild to moderate smog will sweep central and southern parts of northern China as well as western and northern parts of Yellow and Huaihe river basins, said the National Meteorological Center (NMC). Some localities may suffer several smog.

Beijing issued orange alert Friday for air pollution in the coming days, advising children and the elderly to stay indoors, certain construction activities be suspended and heavy vehicles be pulled off the road.

The average density of PM2.5 in Beijing was 58 micrograms per cubic meter last year, meeting the target and 20.5 percent less than in 2016, according to Beijing environmental protection monitoring center.