China's air pollution again at danger levels.

Dangerously high pollution levels have shrouded Beijing in smog for the second time in about two weeks, forcing airlines to cancel flights because of poor visibility and prompting the city government to warn residents to stay indoors.

The outlines of buildings in the Chinese capital receded into a white mist as pedestrians donned face masks to guard against the thick, caustic air. The US embassy reported a level of PM2.5, one of the worst pollutants, at 526 micrograms per cubic metre, or "beyond index", and more than 20 times higher than World Health Organisation safety levels over a 24-hour period.

The Beijing city government advised residents to stay indoors as much as possible because the pollution was "severe". It said that because there was no wind, the smog probably would not dissipate quickly.

Visibility was less than 100 metres (109 yards) in some areas of eastern China, the official Xinhua news agency reported. Air China cancelled 14 domestic flights in or out of the Beijing airport, and an airport in the eastern city of Qingdao was closed, cancelling 20 flights.

The disruptions came in the first week of the country's peak, six-week period for travel, linked to the 10 February lunar new year. Every year, China's transport system bursts at the seams as tens of millions of people travel for the holiday, in the world's largest seasonal migration of people.

Celebrity real estate developer Pan Shiyi, who has previously pushed for cities to publish more detailed air quality data, called for a clean air act on Tuesday and said he would use his status as a delegate to the National People's Congress to propose such legislation.

In less than three hours, his post was forwarded more than 2,300 times and received 14,184 votes, with 99.1% in favour.

Beijing also had exceptionally high pollution two weeks ago, with the US embassy readings of PM2.5 reaching as high as 886 micrograms per cubic metre.

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Cold weather, lack of wind and a dearth of environmental regulations have lately created a perfect storm of toxic smog in northern China. Air pollution has gotten so extreme in China's capital, ABC News reports, that "it is literally off the charts: more than 20 times the maximum safety level."

Some of Beijing's factories are temporarily closing, flights are being cancelled and emergency rooms are filling up with people having severe respiratory reactions to the toxic air they have been breathing.

According to a report on ABC World News, the air quality index in Beijing has reached a height of 755. Higher numbers mean worse pollution, and anything over 300 is considered "an emergency." By comparison, the worst-polluted city in the U.S., Bakersfield, California, reached a peak air quality index of 159 last year.

Perhaps most notably, the notoriously silent Chinese government has recently sent out emergency warnings about the air quality in Beijing for the first time. But many Chinese citizens clearly feel that not enough is being done, according to ABC:

The air is so bad that wealthy Chinese entrepreneur, Chen Guangbiao, is selling fresh air in soft drinks cans, similar to bottled drinking water. Each can is sold for 5RMB or about 80 cents. Chen is well known for his charitable donations and publicity stunts. He says he wants to stimulate awareness of environmental protection among government officials and citizens by selling the canned fresh air.

"If we don't pay attention to environmental protection, in 10 years every one of us will be wearing gas masks and carrying oxygen tanks on the streets," Cheng told ABC News. "By that time, my canned fresh air will be a necessity for household," he predicts.

Sound familiar? In the 1987 comedy Spaceballs, a Star Wars spoof, a corrupt president uses up all the air from his world, and then schemes to steal fresh air from another planet. In this scene, he outwardly denies the crisis while sucking down cans of "Perri-air: canned in Druidia, naturally sparkling, salt-free air."

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