BEIJING - Beijing Municipal air pollution emergency response office on Tuesday issued a yellow alert for smog, reminding residents to take precautions against it.

The air pollution will persist until Thursday. The central part of the Beijing-Tianjin-Hebei region is forecast to see moderate to severe air pollution during the period, said a source with the Beijing Municipal Bureau of Ecology and Environment.

The yellow alert is issued when the air quality index surpasses 200 or the average density of PM2.5 stays above 150 micrograms per cubic meter for two consecutive days.

Under Beijing's current three-tier warning system, the yellow alert is the least severe, followed by orange and red.

The yellow alert and above will trigger a series of compulsory emergency responses including the suspension of outdoor construction operations to reduce dust, the restriction of heavy pollution vehicles or the suspension of production in smokestack industries.