A cloud of dust and sand engulfs Zhangye, Gansu province, on Sunday. Photo: VCG

Police inspect a truck during the sandstorm at a border checkpoint in Erenhot, Inner Mongolia autonomous region, on Monday. Photo: VCG

A yellow wall of sand hits Alxa League, Inner Mongolia autonomous region, at 5 p.m. on Sunday. Photo: Screenshot from CCTV.com

Sand and dust shroud landscape along the Yellow River in Lanzhou, Gansu province, on Monday. Photo: VCG

Residents wearing masks walk over a bridge in Lanzhou on Monday. Photo: VCG

Visitors take boats on the Yellow River during the sandstorm on Monday. Photo: VCG

Visitors walk along the Yellow River during the sandstorm on Monday. Photo: VCG