On Tuesday morning, air quality index readings were at a "hazardous" level of 495 for health-threatening particles with a diameter of less than 2.5 micrometres, or PM2.5.
The Beijing Municipal Environmental Monitoring Centre says pollution across Beijing is severe and expected to persist because there is little wind to disperse pollutants. It advises city residents to stay indoors as much as possible.
Air quality index readings in much of downtown Beijing, as measured by the local environmental watchdog and the US embassy, shot above 350 yesterday - a significant increase from Sunday.
The US embassy's air quality readings, published hourly on its Twitter feed, showed the level of PM2.5 rose drastically throughout the day to 496 at 4pm- far above the "hazardous" level of 300 micrograms per cubic metre.
The Beijing Municipal Environmental Centre, which is under the city's Environmental Protection Bureau, rated air quality in most of the city as being seriously polluted, as PM2.5 readings fluctuated between 340 and 360.
When the level of PM2.5 in the air surpasses 100, it is deemed unhealthy for people with heart or lung disease, older adults and children, and those groups should reduce prolonged or heavy exertion, particularly outdoors, according to advice given by the US Embassy.
Traffic moves slowly through the city amid low visibility. Photo: Simon Song
The smog also appeared to have spread farther to south
The smog also appeared to have spread farther to southeastern regions, with flight disruptions being reported yesterday morning at 10 mainland airports, including in Hebei's Shijiazhuang and Henan's Zhengzhou .
Visibility at the Shijiazhuang airport was reduced to around 100 metres, forcing the cancellation of at least seven flights, and in Zhengzhou more than 10,000 passengers were stranded by 11.30am, as up to 150 flights were either cancelled or delayed, China National Radio reports.