A dust storm enveloped a swathe of northern China yesterday dragging down air quality and visibility and prompting warnings for children and old people to stay indoors.
At least 48 flights were cancelled, including six international routes in Asia and Russia, according to the Beijing Capital Airport's website.
Spring is China's dust-storm season, when winds whip across the Gobi Desert picking up fine sand and dust particles and dumping them along a belt of heavily populated land further south.
The official People's Daily said the worst of the storm would be concentrated on a remote area along the Mongolian border, but that Beijing and locations as far away as the remote northeast of China would be affected for at least 24 hours.
Official data from the Beijing government showed average readings of small breathable particles known as PM 2.5, a major component of China's air quality index, had risen to 630 micrograms per cubic metre in parts of the city by yesterday morning, though it dropped slightly later in the day.
The World Health Organization recommends concentrations of just 10 micrograms.
The city government said the storm would affect the capital until this afternoon when air quality would improve as a high pressure system moved in.
State television said old people and children should stay inside to avoid the worst effects.
The dust storm underlines the environmental problems China faces, added to concern about choking smog from coal powered power plants and factories that also periodically covers much of north China.