BEIJING - Dense fog shrouded Beijing Sunday evening, causing experts and the public to worry about a likely drop in the capital's air quality.

The Beijing Meterological Center on Sunday afternoon issued a code yellow alert to warn about fog in the capital, saying visibility would drop to less than 500 meters in most parts of the city.

The misty weather is forecast to persist over Sunday night and into Monday, according to the center.

The thick fog came just two days after Beijing residents welcomed the city's first snow this winter, replacing their excitement with concerns over worsened air pollution.

Beijing's air quality stood at grade II on Saturday and Sunday, said Beijing Municipal Environmental Protection Bureau. The results, however, would be threatened by the lingering fog in the following days, it admitted.

As of Sunday evening, poor visibility from the fog has forced several highways surrounding Beijing to be temporarily closed, and traffic authorities have also warned of extended gridlock in the city.