A combination picture shows Beijing's smoggy air beginng to clear since Jan. 15. [Chinanews.com]

Although Beijing's smoggy air began to clear late Monday due to a light snowfall, the city's air pollution remains at high levels.

The snow, which lasted until 7 a.m. Tuesday, reduced the concentration of fine particulate matter in the air to 50 to 70 micrograms per cubic meter, according to the data released by the city's environmental monitor center.

The city's weather bureau lifted its fog alert at 6 a.m., with visibility in most areas increasing to more than 10 km by 3 p.m., the bureau said.

Air quality indices reached the "medium to dangerous level" Tuesday morning. The indices were literally off the charts during the preceding five days, exceeding the "maximum" level of 500.

The weather bureau said wind will sweep the city from Tuesday evening to Wednesday. Air quality is expected to improve after the wind disperses the smog.

Lingering clouds of smog have been spotted in many parts of China in recent days, affecting traffic and sending some people to the hospital for respiratory ailments.

Four deaths have been attributed to the smoggy weather, including two high school students who were hit by a train due to low visibility in the city of Chaohu in east China's Anhui province on Monday.

Another two were killed in a pileup involving 20 vehicles in neighboring Zhejiang province early Tuesday morning. Eight others were injured.

The low visibility also prevented authorities from spotting a furniture factory fire in Zhejiang, with the fire raging for four hours late Monday until neighbors spotted the fire and called firefighters. No casualties have been reported in connection with the fire.

Residents in many cities have been advised to stay indoors. Regular outdoor activities, such as morning exercise activities and flag-raising ceremonies, have been held indoors.