A dust storm is choking a large swathe of northern China including the capital, Beijing, in yet another air quality crisis to affect the country.
Official air quality readings have soared well above the recommended World Health Organization (WHO) limit.
Authorities are advising residents to avoid outdoor activity and for children and elderly people to remain indoors.
The dust is blowing in from neighbouring Mongolia and China’s Inner Mongolia Autonomous Region.
Beijing’s environmental agency said that as of 11:00 local time (03:00 GMT), the PM2.5 reading – which measures pollution in the form of small breathable particles – was 500 micrograms per cubic metre.
The WHO says the maximum safe level should be 25 micrograms per cubic metre.
Authorities said Beijing would be affected until Thursday evening and visibility would be noticeably low throughout the day. Dozens of flights have been delayed or cancelled.