Beijing, Safar 17, 1437, November 29, 2015, SPA -- Some of the worst smog of the winter enveloped Beijing Sunday with air pollution levels nearly 15 times the safety limit set by the World Health Organization, according to US figures, dpa reported. 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 356 micrograms per cubic meter at 11 am 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 air-quality index reading earlier hit a winter high of 434 at noon on Saturday. The daily maximum exposure to PM2.5 particles recommended by the WHO is 25 micrograms per cubic metre. --SPA 11:36 LOCAL TIME 08:36 GMT www.spa.gov.sa/w