Beijing residents advised to stay indoors as much as possible with severe pollution at levels 'beyond index'

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.