Air pollution in the Chinese capital Beijing has reached levels judged as hazardous to human health.
Readings from both official and unofficial monitoring stations suggested Saturday's pollution had soared past danger levels outlined by the World Health Organization (WHO).
A BBC correspondent in Beijing says heavy smog has smothered the city for many days and 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, the BBC reports.
WHO guidelines say average concentrations of the tiniest pollution particles - called PM2.5 - should be no more than 25 microgrammes per cubic metre.
Official Beijing city readings on Saturday suggested pollution levels over 400 microgrammes. An unofficial reading from a monitor at the US embassy recorded 800.
The guidelines say air is unhealthy above 100 microgrammes. At 300, all children and elderly people should remain indoors.