Air pollution levels in China's notoriously dirty capital were at dangerous levels Saturday, with cloudy skies blocking out visibility and warnings issued for people to remain indoors.
Local authorities warned that the severe pollution was likely to continue until Tuesday.
The Beijing Municipal Environmental Monitoring Center has reported air-quality indexes between 176 and 442 from its monitors throughout the greater Beijing area since Friday. The index indicates the level of airborne PM 2.5 particulates, which are tiny particular matters considered the most harmful to health.
The air is considered good when the index is at 50 or below, but hazardous with an index between 301 and 500, when people are warned to avoid outdoor physical activities.
Monitors in Beijing reported air quality indexes above 300 on Friday, and the center's real-time reports showed Beijing remained heavily polluted Saturday, with the indexes at or approaching 500 at 5 p.m. from some monitoring stations.
A warning scrolled across the monitoring center's website on Saturday said that the density of PM2.5 had reached 700 micrograms per cubic meter in many parts of Beijing and that the polluted air was expected to linger for the next three days.
Monitors at the U.S. Embassy in Beijing recorded an off-the-chart air-quality reading of 728 as of 4 p.m. Saturday and said the PM2.5 density had reached 845 micrograms per cubic meter.
Readings are often different in different parts of Beijing.
According to rules issued by the city government in December, all outdoor sports activities are to stop and factories have to reduce their production capacity if Beijing's official air-quality index exceeds 500.
Air pollution is a major problem in China due to its rapid pace of industrialization, reliance on coal power, explosive growth in car ownership and disregard to environmental laws.
In Beijing, authorities have blamed foggy conditions and a lack of wind for the high concentration of air pollutants.
Several other cities, including Tianjin on the coast east of Beijing and southern China's Wuhan city, also reported severe pollution over the last several days.