Beijing, Safar 16, 1437, November 28, 2015 -- The worst smog of the winter enveloped Beijing Saturday as air pollution levels reached nearly 20 times the safety limit set by the World Health Organization, according to US figures released by dpa. Authorities in the Chinese capital warned of "severe pollution" and advised the capital's 20 million inhabitants to stay indoors. Beijing's PM2.5 concentration, referring to particles smaller than 2.5 micrometres, reached a high of 434 micrograms per cubic meter at noon on Saturday. That is in the highest band of the scale and is considered "hazardous," according to the US embassy's air-quality index reading. The daily maximum exposure to PM2.5 particles recommended by the WHO is 25 micrograms per cubic metre. --SPA 10:54 LOCAL TIME 07:54 GMT www.spa.gov.sa/w