BEIJING - Air pollution soared in Beijing as the Chinese capital was hit by a huge sandstorm, and dust also shrouded other parts of the country in a sickly orange haze.
The official air quality index in Beijing hit the maximum level of 500, indicating "severe pollution", though some unofficial readings were nearly twice that figure.
Authorities issued weather warnings and warned people to reduce their outdoor activities, as visibility fell to less than one kilometre in some areas of the city on Wednesday morning.
In parts of China's north and northwest, high winds and dust turned the sky a lurid tangerine, appearing to cut visibility to less than a few hundred metres in some places.
Authorities said the pollution was largely driven by airborne particles known as PM10, which are small enough to be inhaled and can aggravate a range of respiratory and other health issues.
China's weather service on Wednesday issued a yellow warning for dust across a sweep of the north and northwest for 24 hours from 8am.
People in affected areas should "do a good job of protecting against wind and sand, and close doors and windows in a timely manner", the weather service said, adding they should also wear masks while outdoors.
Children, the elderly and people with respiratory allergies and other conditions should "limit how much they go out", the service said.
Dust storms are fairly common across northern China in the spring, when changes in the wind kick up grit across the largely arid region.
The current weather system is "the most extensive of the year so far", according to the weather service, adding that it was expected to weaken from Thursday.