BEIJING - A strong cold front is expected to clear up lingering smog in Beijing on Tuesday night, the city's meteorological bureau said Monday.

The Chinese capital has been shrouded in heavy smog for five straight days. As the city's air quality has hovered at hazardous levels, the public has been advised to stay indoors and to avoid strenuous exercise.

The density of PM2.5 -- airborne particles with a diameter of 2.5 microns or less that can deeply penetrate the lungs -- reached over 900 micrograms per square meter at some monitoring stations on Saturday evening.

The municipal meteorological bureau continued to issue the highest alert on smog Monday morning, as the city's downtown and southern areas reported PM2.5 levels of over 250 micrograms per square meter.

Zhang Dawei, head of the Beijing Municipal Environmental Monitoring Center, attributed the poor air quality to heavy pollution in Beijing and its surrounding areas, a greater use of coal to fight the coldest winter in 28 years and a lack of wind.

Beijing implemented its emergency response plan for hazardous pollution for the first time on Sunday.

A total of 58 high-polluting companies were ordered to halt operations, and 41 others cut their emissions by 30 percent on Sunday. Work was also suspended at 28 construction sites, said Li Hong, a deputy director of the municipal commission of economy and information technology.

The cold front will sweep most of China starting Wednesday and disperse the fog that has shrouded a large portion of central and eastern China in recent days, the National Meteorological Center said Monday.

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