Heavy smog covers Beijing on March 16, 2016. (Photo: Xinhua)

Most urban districts of Beijing began to suffer moderate air pollution early Sunday due to weather conditions "not favorable for dispersing pollutants", according to Beijing Youth Daily on Sunday, citing Beijing Municipal Environmental Monitoring Center.

But the pollution is expected to ease on Monday as weak cold air arrives in the Beijing-Tianjin-Hebei region, the pollution watchdog told the newspaper.

China has a six-level air pollution system depending on the air quality index (AQI). Excellent air requires index levels below 50, and if the index falls between 151 and 200, the day is classified as moderately polluted. Days when the index rises over 300 are considered severely polluted.

According to the center's official Weibo account, the index in southeast Beijing reached 141 by 8 am on Sunday. Northwest and northeast Beijing reached almost 130.