Sandstorm engulfs Chinese Zhangye City
Video from state broadcaster CCTV showed a grey wall of sand hitting Zhangye City in Gansu province on Sunday, casting a yellow fog across the city.
Images from official news agency Xinhua showed residents covering their faces in scarves as they went about their daily lives.
Visibility went below 100 metres (328 feet) in parts of the city and police were deployed to ensure safety along the expressways, CCTV said.
Vehicles were made to slow down and police in high visibility vests were seen directing traffic.
Winds also sparked fires in rural areas when heating kindle was blown onto haystacks.
Authorities in the city also put out an advisory warning of dry weather and a risk of fire, telling residents to "take precautions".
While the Northwest faced a sandstorm, Beijing was on Monday shrouded in a thick smog that prompted many to wear protective face masks.
Levels of small particulate matter, known as PM 2.5, hovered around 360 in the afternoon, according to air quality monitoring website aqicn.org, or nearly 15 times the World Health Organisation's recommended daily maximum exposure.
According to Xinhua, a sandstorm is also forecast to be hitting Beijing from the northwest.
(With inputs from agencies.)