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Beijing residents woke up to yellow sky on Sunday morning as northern China   (hit) by the largest sandstorm of the decade.

Air pollution readings rose to the upper limit of 500 at 8 a.m. according to data from the city's environmental monitory center, as visibility was reduced to  (little) than 1,000 meters in parts of the city.

The city's weather bureau advised residents to stay indoors as much as possible, while experts are working to find out  the sandstorm came into being.