BEIJING, Jan. 11 (Xinhua) -- A new round of smog will affect Beijing and neighboring provinces from Friday, data from the China National Environmental Monitoring Center showed Thursday.

The Beijing-Tianjin-Hebei region and Shandong, Shanxi, Henan provinces will be hardest hit from Jan. 12 to 17.

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

The alert, the second highest level, will come into effect in Beijing from Saturday and last until Monday, said the city's air pollution emergency response office.

From Jan. 13 to 15, parts of the Beijing-Tianjin-Hebei region, southern Shanxi, western Shandong as well as northern Henan are forecast to see severe air pollution, with the density of PM2.5, the major air pollutant, estimated to exceed 250 micrograms per cubic meter of air, said the Ministry of Environmental Protection.

The air will gradually improve on Jan. 16, but worsen again the next day. The smog will be dispersed when a cold front arrives on Jan. 18, the ministry said.

According to the local air pollution emergency response plan, an orange alert should be issued when the average air quality index is forecast to exceed 200 for three consecutive days and one of those days is forecast to be over 300.

Under China's four-tier warning system, red is the most severe, followed by orange, yellow and blue.