BEIJING — Tons of sand turned Beijing's sky orange as the strongest sandstorm this year hit northern China, a reminder that the country's expanding deserts have led to a sharp increase in the storms.
The sky glowed Saturday and a thin dusting of sand covered Beijing, causing workers and tourists to muffle their faces in vast Tiananmen Square. The city's weather bureau gave air quality a rare hazardous ranking.
Air quality is "very bad for the health," China's national weather bureau warned. It said people should cover their mouths when outside and keep doors and windows closed.
China's expanding deserts now cover one-third of the country because of overgrazing, deforestation, urban sprawl and drought. The shifting sands have led to a sharp increase in sandstorms — the grit from which can travel as far as the western United States.
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The Chinese Academy of Sciences has estimated that the number of sandstorms has jumped six-fold in the past 50 years to two dozen a year.
The latest sandstorm also hit the regions of Xinjiang and Inner Mongolia and the provinces of Shanxi and Hebei, affecting about 250 million people over an area of 312,000 square miles, the state-run Xinhua News Agency reported.
As the sandstorm moved southeast, South Korea's national weather agency issued a yellow dust advisory for Seoul and other parts of the country.
Chun Youngsin, a researcher at the Korea Meteorological Administration, said the yellow dust was expected to hit the Korean peninsula beginning Saturday afternoon and it would be "the worst yellow dust" this year.
Some flights at Beijing's international airport were delayed but eventually took off, said a woman answering phones at the airport hot line.
Skies cleared in the city by midday, but a warning of more dusty weather remained in place until early this afternoon.
"I think this kind of natural disaster is caused by human activity, but I don't know the exact reason, and I don't know exactly what we can do to prevent this," said Beijing resident Shi Chun yan.