Pollution in Beijing was stuck at unhealthy levels for the sixth straight day, prompting warnings for people to stay indoors as thick grey smog shrouded the capital a week before the annual meeting of China's legislature.

The concentration of PM2.5, the small particles that pose the greatest risk to human health, hit 462 at 5 p.m., according to a U.S. Embassy pollution monitor. The World Health Organization recommends day-long exposure levels of 25, and the last time PM2.5 dropped below 150 in Beijing was Feb. 19.

Beijing last year - pollution levels are running almost 20 times acceptable WHO standards. Credit:Reuters

The heavy smog in Beijing may draw new scrutiny to government pledges to ease pollution around the country as leaders gather for the meeting of the National People's Congress that begins March 5. At the end of last year's event, Premier Li Keqiang promised to clean up pollution and said smog gave him a “heavy heart.”

In a bid to fight Beijing's pollution, 147 industrial companies have cut or suspended production, the Xinhua News Agency reported yesterday, citing the Beijing Municipal Economic and Information Commission. In Liaoning and Shandong provinces, visibility fell to less than 50 meters and expressways were closed, Xinhua said.