Millions of people across eight Chinese provinces were advised to wear masks outside as a sandstorm engulfed the region.
Visibility dropped to as low as 100 metres in Hebei Province and warnings were issued to motorists and aircraft to take extra precautions.
In Beijing, one air quality index gave a reading of 800, on a scale where anything over 150 is considered unhealthy.
Dangerous sandstorms occur when high winds start to lift dust and dirt mixed with industrial pollution, with the potential to spread across a vast area.
Experts suggest this latest storm originated in Mongolia, where heavy deforestation and overgrazing has led to an increase in desert-type land masses.