BEIJING - The Chinese metropolis of Wuhan was blanketed by thick yellowish cloud Monday, raising fears of pollution among its nine million inhabitants, residents told AFP.
Witnesses said the haze appeared suddenly in the morning, and residents rushed to put on face masks.
"I looked out of the window of my office and I could not believe my eyes," said Li Yunzhong, describing the haze as opaque, with yellowish and greenish tinges.
"At first I thought it was going to rain but it wasn't fog. In 31 years in Wuhan I have never known anything like it. We are very worried because we do not know what it is."
France's consulate-general in the central city advised residents to stay at home, close their windows and limit the use of air-conditioning.
It said on its website: "The source of the thick cloud that has covered the city of Wuhan since this morning is at present unknown.
"Local authorities have promised us the information as soon as possible."
Air pollution is increasingly acute in major Chinese cities and authorities are frequently accused of underestimating the severity of the problem in urban areas, especially in Beijing.
Official statistics are sometimes at odds with non-government measurements, and are often viewed with distrust.