Residents of central China’s largest city have been advised to stay indoors after a thick orange haze blanketed the city.
Locals described the mist as thick, opaque and smelling of smoke, saying it suddenly descended on several cities in Hubei province on Monday morning.
The internet was immediately awash with rumours of an industrial accident or explosion at a chemical complex in the north east of Wuhan, but the official Xinhua news agency denied this, blaming the fog on straw burning.
Hubei province’s environmental protection department was quoted as saying: "Children, the elderly and people with heart or respiratory diseases are advised to stay indoors." Those venturing outside were advised to wear a protective mask.
Li Yunzhong, a Wuhan resident, said: "I looked out of the window of my office and I could not believe my eyes.
At first I thought it was going to rain. In 31 years in Wuhan I have never known anything like it. We are very worried because we do not know what it is."
Yesterday local police posted an announcement online saying they had detained two individuals they believed had been spreading rumours about the haze online.
Police claimed the users had "caused panic among the netizens," by saying the haze had been caused either by a chlorine leak at a chemical factory, or by an explosion at a steel plant. Police advised people to be wary of the rumours.
An air quality monitor reported that Wuhan’s PM10 particulate concentrate stood more than triple its daily average. The report also quoted the environmental protection department, saying industrial accidents were not responsible for the haze and analysis showed an increase in carbon particles from burning organic matter.
Many residents doubted this official explanation however, with one saying "We don't practice large-scale shifting agriculture in our region."
Other residents were said to be fleeing the city in a bid to escape the cloud.
Wuhan, the capital of Hubei province, is the largest city in central China and home to many foreign factories, including the French automotive group PSA Peugeot Citroën.