BEIJING - The Beijing municipal government has issued a yellow alert for heavy air pollution which came into force from 4 pm Thursday.

Unfavorable weather conditions are blamed for the smog blanketing Beijing and neighboring regions from Wednesday to Saturday, according to the city's weather and ecological environment authorities.

The first snow of the winter has also been forecast to hit the city over the weekend.

Under China's four-tier warning system for air pollution, red is the most severe warning, followed by orange, yellow and blue.