18 December 2015 (BBC) – Beijing has issued a second pollution red alert, little more than a week after the first ever such warning.
The Chinese capital will see hazardous smog from Saturday until Tuesday, the official meteorological service said.
Nationwide, a vast area from Xian in central China to Harbin in the north-east would also be badly hit, the National Meteorological Centre said.
Beijing authorities have advised residents to avoid outdoor activity and for schools to stop classes.
The red alert - the highest of a four-level alert system instituted two years years ago - also triggers restrictions on vehicle use, factories and construction work.
The government has promised to take action to address often dangerous levels of pollution.
Long-term exposure to high levels of PM2.5 - the dangerous particulate matter in smog - has been linked to lung damage and respiratory illnesses.
The World Health Organization considers PM2.5 readings of 25 micrograms per cubic metre as the maximum safe level.
The smog which hit Beijing on 8 December peaked just below 300. Residents are encouraged to stay indoors if levels exceed that level. […]
Coal-powered industries and heating systems - in heavy use during the cold Beijing winter - are major contributors to the smog.
It is made worse by weather conditions and the city's geography - it is bordered to the south and east by heavily polluting industrial areas, and to the north and west by mountains that trap the dirty air over the city. [more]