Beijing warned the young, elderly and ill among its 20 million inhabitants to stay indoors as air pollution exceeded World Health Organization-recommended levels by more than 10 times today.

The concentration of PM2.5, fine air particulates that pose the greatest health risk, was 260 micrograms per cubic meter at 10 a.m. near Tiananmen Square, compared with an average of 188 over the past 24 hours, the Beijing Municipal Environmental Monitoring Center said on its website. The WHO recommends 24- hour exposure to PM2.5 concentrations no higher than 25 micrograms per cubic meter.

With environmental concerns now a main cause of social unrest, the government has pledged to cut coal consumption, shut steel plants and control the number of cars on the road to ease smog. The poor air quality in Beijing marked a reversal from a trend in which pollution levels had declined by about 25 percent from Nov. 16 to Dec. 15, according to a Dec. 21 article in the Beijing News newspaper.

A monitoring station at the U.S. Embassy showed PM2.5 levels at 211 as of 10 a.m., with air quality at “hazardous” levels.

Air pollution in almost half the city was rated “heavy,” the second worst rating on the Beijing Municipal Environmental Monitoring Center’s six-level scale. At that level, the city recommends children, the elderly and people with heart and lung ailments stay indoor and people limit outdoor activities.

Pollution will ease starting at around 12 p.m. tomorrow, the center said.

Shanghai, 670 miles (1,080 kilometers) southeast of Beijing, reported record levels of smog earlier this month, causing flight cancellations and prompting the government to order vehicles off the road and warn children to remain indoors. The PM2.5 reading in Shanghai was 164.5 micrograms per cubic meter as of 10 a.m. and air quality was ranked “lightly polluted.”

Feifei Shen. Editors: Nicholas Wadhams, Gregory Turk

To contact Bloomberg News staff for this story: Feifei Shen in Beijing at To contact the editor responsible for this story: Nicholas Wadhams at

Photo Credit: A plane flies in the polluted air above the airport fences in Beijing February 22, 2012. Petar Kujundzic / Reuters