Caution urged as Beijing smog levels skyrocket

Residents of China's capital, Beijing, have been warned to take precautions after air pollution readings soared. Readings on Thursday registered more than 20 times the recommended exposure levels by the World Health Organisation (WHO).

Background:
Officials advise those going to work to wear protective masks [BBC]
Severe smog in north China prompts warnings to stay inside [Bloomberg News]
Highways closed as Beijing blanketed by toxic smog [RT]