Beijing is experiencing air pollution that has reached levels considered hazardous to human health, say experts.
According to readings from both official and unofficial monitoring stations, pollution has soared past danger levels outlined by the World Health Organization (WHO), reports the BBC.
Heavy smog has smothered Beijing for many days. The air tastes of coal dust and car fumes, two of the main sources of pollution.
Economic growth has left air quality in many cities notoriously poor.
WHO guidelines say average concentrations of the tiniest pollution particles - called PM2.5 - should be no more than 25 microgrammes per cubic metre.
Air is unhealthy above 100 microgrammes. At 300, all children and elderly people should remain indoors.
Official Beijing city readings on Saturday suggested pollution levels over 400. Unofficial reading from a monitor at the US embassy recorded 800.
Once inhaled, the tiny particles can cause respiratory infections, as well as increased mortality from lung cancer and heart disease.
Last year Chinese authorities warned the US embassy not to publish its data. But the embassy said the measurements were for the benefit of embassy personnel and were not citywide.