Beijing issued a warning for heavy fog on Monday afternoon after joyously greeting the winter's first snowfall just a few hours earlier.

Motorists were advised against careless driving as the capital was hit by a thick fog that reduced visibility to less than 500 meters, according to the Beijing Municipal Meteorological Observatory.

Air quality was designated "moderately polluted" downtown and "heavily polluted" in the suburbs, according to the observatory.

It forecast that the fog would disperse after midnight when a cold front would reach Beijing. The sky would be clear Tuesday.

The snow-triggered fog delayed about 130 flights at the Beijing Capital International Airport through midday, but no expressways had shut down by early evening.

The snow started to fall at 4:30 a.m., covering most of the city. The average precipitation was 1 mm, with a maximum 2 mm registered in the southern suburbs as of 8 a.m., said Guo Hu, director of the Beijing Municipal Meteorological Bureau. The snow stopped at noon.

Beijing usually receives its first snow in late November, so Monday's snowfall came a little late, Guo said.

Visibility on roads decreased to less than 500 m in some urban areas, causing traffic jams on more than 100 streets as of 9 a.m.. Vehicles were running very slowly on another 80 roads.

The combination of heavy fog and accidents brought traffic to a standstill for many vehicles coming to the capital from Chengde, Hebei Province, on a key expressway.

More than 1,890 workers and 450 vehicles from the city's public sanitation department were mobilized to clean up streets, using more than 745 tons of chemical powder and 1,832 tons of liquids to melt the snow.

The amount of melting agents was restricted in an effort to reduce side effects to roads and traffic, according to sanitation officials.

More than 300 workers and 230 vehicles were involved in snow removal on Chang'an Avenue and the Second and Third Ring roads in the downtown area.

The city's public transport company dispatched 100 teams to keep routes clean and safe. Some 300 buses were on standby to meet the possibility of higher transport demand, and Beijing's subways served more passengers than usual during the morning rush hour, forcing the Metro administration to send out more workers to maintain order.

Winter weather affected travel in other parts of the country as well on Monday. Heavy fog forced closure of a number of expressways in northeast China's Liaoning Province and northern Shanxi Province.

Eight flights were delayed in an airport of Taiyuan, capital of Shanxi Province. In Urumqi, capital of northwest China's Xinjiang Uygur Autonomous Region, more than 200 flights were delayed or canceled, affecting more than 4,000 passengers.

Between 400 and 600 passengers were still waiting for their delayed flights at 8:15 p.m. at the Urumqi International Airport, while the others have departed since fog dissipated at 12:30 a.m. and then flights resumed.

(Xinhua News Agency, December 11, 2007)