BEIJING, Oct. 26 (Xinhua) -- The heavy fog continued to shroud Beijing continued and got thicker on Friday after the municipal observatory issued a fog warning on Wednesday night and another one at 5:00 a.m. Friday morning.

The visibility in the downtown area is less than 200 meters. The observatory predicted that the fog would hang over for six hours, and is expected to clear off by Friday night, when a current of cold air brings drizzle and breeze to the city.

The heavy fog caused closure of all major highways linking to the national capital and the eastern part of the city's sixth ringroad.

There was no serious traffic jams in the morning rush hour since residents had been aware of the bad weather, and many people turned to public traffic instead of driving their own cars for safety reasons.

The thick haze and stagnant air exacerbated the city's pollution. Sun Jisong, the chief weatherman with the municipal observatory warned seniors and children to stay indoors to avoid contracting respiratory diseases.