Heavy fog hung over Beijing for the fourth consecutive day Saturday, closing?five interprovincial expressways and?threatening to dampen the environmental watchdog's ambition to keep Beijing's sky clear.

Daily air quality reports released by the China Environmental Monitoring Center indicated Beijing's air was polluted for four consecutive days since Wednesday. [jinghua.cn]?

The foggy weather began on Wednesday in Beijing and the neighboring Tianjin municipality and Hebei Province.

At least five interprovincial expressways in Beijing were closed early Saturday for safety considerations, including the expressways linking to Harbin in the northeastern province of Heilongjiang, Shanghai, Hong Kong, Tianjin and Hebei.

Parts of the Sixth Ring Road in outer Beijing were also closed briefly but reopened later Saturday morning, the Ministry of Transport said.

Complaints of the foggy weather spread quickly on the Internet, as the mist and subsequent congestion dampened many people's plans for weekend outings.

"It's been seven hours and I'm still stranded on the road. I wish I could arrive in Beijing soon," said Internet user Hao Changkun from Langfang, a small city in Hebei Province, which is within an hour's drive from Beijing under normal circumstances.

Traffic was at a standstill on many Beijing roads, as many people, unprepared for the fog, chose to climb mountains in the suburbs and enjoy the maple leaves that turn red in fall.

Beijing's traffic police said the fog exacerbated existing congestion triggered by the popular "red leaves festival" in mountains in the city's western and northern suburbs from now to mid November.

Meanwhile, the foggy weather threatens to dampen the environmental watchdog's ambition to keep Beijing's sky clear.

Daily air quality reports released by the China Environmental Monitoring Center indicated Beijing's air was polluted for four consecutive days since Wednesday.

Beijing has reported 234 "blue sky days" so far this year, still 41 days to go to meet the year's target of 275 days, according to the city's environmental protection bureau.

Beijing's "blue sky days" target is aimed at keeping the mega-city's air pollution under close watch.