China is the world's top textile exporter due to smog that has blanketed the north of the country in the past few days, cotton mills have stopped buying raw cotton and have suspended output in Hebei and parts of Shandong, the two Chinese provinces both major growing regions for the fibre, as part of measures to curb smog, according to a report by Cncotton.com, a government-backed trade website.

However, the report did not reveal the number of mills affected, nor give details on the amount of production involved. The report said that cotton processing in parts of Hebei, one of the nation's most polluted provinces, may be affected until the end of December.

The shutdowns come as more than more than 40 cities in China's northeast have issued pollution warnings in the past 48 hours. For many cities, that means shutting factories, closing schools, recommending residents stay indoors and curbing traffic and construction work.

China's most-active cotton futures on the Zhengzhou Commodity Exchange after earlier hitting their lowest in a month at 15,465 yuan at the beginning of this week saw settling down 0.60 percent at 15,715 yuan ($2,263.27) per ton.

But the prolonged closures at cotton mills likely to hurt demand for the natural fibre amid concerns about global oversupply.

Pollution alerts have become increasingly common in China's northern industrial heartland, especially during winter when energy demand - much of it met by coal - skyrockets.