BEIJING - China's weather observatory issued an yellow alert on Tuesday morning for smog in the north of the country that will linger until Wednesday.

Beijing, Tianjin and the neighboring provinces of Hebei, Henan, Shanxi, Shandong, Shaanxi and Sichuan will face air pollution, with southern Beijing and southwestern Hebei expected to face heavy smog, according to the National Meteorological Center (NMC).

China has a four-tier warning system, with red as its most severe level, followed by orange, yellow and blue.