The Beijing-Tianjin-Hebei cluster will be engulfed in heavy haze from Friday to Monday due to weather conditions that don't favor the dispersal of airborne pollutants, authorities said. 

The Ministry of Ecology and Environment said in a news release on Friday that the southern part of the Beijing-Tianjin-Hebei region, western Shandong province, and northern Henan province will be the first areas affected on Friday, experiencing moderate pollution. 

More areas will be enveloped in smog as the pollution worsens due to temperature inversion, which prevents the atmosphere from circulating normally, and high humidity. 

Most cities in the cluster will experience moderate to heavy haze from Sunday to Monday. 

The cluster includes 28 major cities in Hebei, Shandong, Shanxi and Henan provinces, as well as Beijing and Tianjin, and coordinated action will be taken to control air pollution. 

The density of PM2.5 — airborne particles with a diameter of 2.5 micrometers or less that can invade even the smallest airways — is expected to peak at 200 micrograms per cubic meter or higher from Sunday night to Monday morning. 

The pollution will be alleviated on Tuesday thanks to cold air from the north. 

The ministry has notified all governments from six provincial-level regions in the cluster, urging them to launch emergency responses, including restricting or suspending production in smokestack industries to curb pollution. 

An orange alert has been triggered for air pollution in Hebei province. Beijing authorities have also issued a yellow alert for noon on Saturday. 

Under the four-tier warning system, the blue alert is the least severe, followed by yellow, orange and red. However, there is no blue alert in Beijing's warning system.