Air quality in Beijing and other areas of northern China is reaching dangerous levels due to smog conditions and sandstorms. NBCNews.com's Dara Brown reports.

BEIJING — Beijing and other parts of northern China were stung by hazardous air pollution levels Thursday as strong winds blew a sandstorm through the region.

Air in the capital turned a yellowish hue as sand from China's arid northwest blew in, turning the sky into a noxious soup of smog and dust.

At 6 a.m. local time, the U.S. Embassy's air quality index showed a reading of 516 for particles less than 2.5 micrometers in diameter. Known as PM2.5, such particles are considered particularly dangerous because they can lodge deeply in the lungs. On the American air pollution index, the air at that time and throughout much of the morning was classified as "beyond index."

Feng Li / Getty Images A composite photograph shows Beijing's skyline during Thursday's sandstorm, top, and during good weather on Feb. 19.

The developers of the U.S Embassy's air monitoring station had planned for an index capped at 500. The World Health Organization suggests that 24-hour exposure to PM2.5 should be limited to levels of 25 on that scale.

Beijing's municipal government issued a yellow-haze warning late Wednesday while state media urged citizens to stay indoors or to take precautions such as donning face masks before venturing outside.

Across northern China in provinces including Hebei, Hubei, Jiangsu and Inner Mongolia, air monitoring stations recorded readings over 500, and visibility across the region was severely curtailed. In some places visibility was below 3,200 feet, leading to highway closures, suspension of high-speed train services and the cancellation of flights from Beijing International Airport.

By mid-afternoon, pollution levels had fallen and strong winds had pushed much of the remaining cloud cover from the capital.

Geographically close to the Gobi Desert, Beijing and other northern cities are particularly susceptible to sandstorms such as Thursday's. Sandstorms are prevalent in late winter and spring as melting frost frees sand and strong winds kick it up and push it eastward.

The start of 2013 has brought chronic bad air to much of China. In January, air pollution readings were so bad that they were compared to living in an airport smoking lounge. That comparison was underscored by record high levels of PM2.5 on Jan. 12, when readings topped out at 755 on the air quality index.

Frustration over China's continued pollution problems popped up across Chinese social media. But irritation over the long-brewing issue was perhaps best summed up by a viral photo originally posted on popular Web portal QQ.com of an unhappy looking Yao Ming, grimacing at the Beijing sky.

Adrian Bradshaw / EPA People in Beijing endure a noxious and potentially dangerous mix of sand and fine particulate pollution on Thursday, after a sandstorm blew in from the Gobi Desert.

Yao, the former NBA All-Star and current member of a Communist Party advisory board known as the China People's Political Consultative Conference, is currently in Beijing in the lead-up to next month's National People's Congress.

The congress will mark the final step in China's once-in-a-decade leadership change as party heads Xi Jinping and Le Keqiang formally take over as China's president and prime minister, respectively.

Since taking over China's ruling Communist Party late last year, the new leaders have spoken repeatedly about improving the mainland's environment.

Many China watchers believe that China's environmental degradation -- underscored by severe air pollution, contaminated soil and dirty waterways -- will be a focal point during the congress.

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