Chinese media say air quality in Beijing has fallen significantly due to thick fogs and smog.

Local media report that smog has continued for the third day and air quality has deteriorated to the lowest point this winter.

The air pollution index in most areas in Beijing exceeded 300 points on Thursday, indicating heavy pollution and ranking the highest among 113 major cities worldwide.

Beijing city officials issued a "yellow" advisory Thursday afternoon. Five-hundred is the highest and most dangerous reading on the Chinese air pollution index.