Update: As of 11:00am on Wednesday, the Web site of Beijing's Capital International Airport  shows that about a dozen domestic flights between Beijing and major northern Chinese cities have been cancelled or delayed. Up to 15 international flights have been cancelled. Affected destinations include Tokyo, Istanbul, Moscow, Kuala Lumpur, Chicago, Franfurt and Helsinki.
Thick smog covered almost one seventh of China yesterday, causing traffic chaos on highways and disruptions at airports.
The Ministry of Environmental Protection said satellite images showed smog covering an area of 1.3 million square kilometres by 10am, a third more than on Monday and spanning more than 10 municipalities and provinces.
Serious air pollution was recorded in northern cities such as Beijing and Shijiazhuang and southern cities such as Wuhan and Chengdu .
It was the first time the ministry had released satellite data on the extent of smog, which had also plagued China on three other occasions this month, but it did not release the actual images.
Satellite images released by the US space agency Nasa drew millions of clicks from mainland internet users.
"Beijing shrouded in smog" Video by Simon Song
In Beijing, the government's air pollution index topped 400, three times higher than the national health guideline. The worst reading, 454, was taken at the National Olympics Sports Centre in the Chaoyang district at 4pm, with levels of PM2.5 - fine respirable particulates - reaching 421 micrograms per cubic metre, nearly 17 times the maximum recommended by the World Health Organisation.
The US embassy's air quality index reading for Beijing stood at 475 and "hazardous" at noon after reaching 517 - "beyond index" - at 6am.
There was traffic chaos in many regions. The Ministry of Transport said Beijing shut down nine highways. Hebei closed five as visibility in some areas dropped below 50 metres, and Hubei shut one highway after three cars crashed in Wuhan due to poor visibility, killing one and injuring 15.
Airlines were also affected. Beijing Capital International Airport reported the cancellation of more than 50 flights. At Xinzheng International Airport in Zhengzhou , Henan, nearly 400 flights had been delayed or cancelled over the past two days.