Beijing has been enveloped by a dense grey smog as the capital experienced the season's first wave of extremely dangerous pollution, with toxic particles registering more than two dozen times the level considered safe.
The air took on an acrid odour, and many of the city's commuters wore industrial strength face masks as they hurried to work.
"I couldn't see the tall buildings across the street this morning," said a Beijing traffic co-ordinator. "The smog has gotten worse in the last two to three years. I often cough, and my nose is always irritated. But what can you do? I drink more water to help my body discharge the toxins."
A monitoring post at the US Embassy in Beijing recorded pollution levels about 26 times higher than those considered safe by the World Health Organisation.
The city's air quality is often poor, especially in winter when stagnant weather patterns combine with an increase in coal-burning.
In recent years, China has beefed up regulations and pledged financial resources to fight pollution.
Beijing authorities said the haze on Thursday has reduced the visibility to several hundred metres and that the severe pollution is likely to continue through Friday.