China's capital issued a yellow alert for heavy air pollution starting from Saturday at noon due to local pollution accumulation and regional pollution transmissions, Beijing Daily mobile app reported Friday.

The air quality will start to improve gradually starting from Monday night when meteorological conditions are expected to provide a better environment for diffusion.

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

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.

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.