Authorities in China’s far west have bred and trained "an army" of silver foxes bought from a fur farm to fight a plague of rats threatening a huge expanse of grasslands, state media said on Wednesday.

The Xinjiang government bought 20 foxes in 2004 and they have since increased to 284 and been released into the wild, the official Xinhua news agency said.

“Foxes are excellent natural predators of the rodent. One fox can catch about 20 rats per day. There has been a decline in the rat population in several counties where the measure has been adopted,” it quoted official Ni Yifei as saying.

Rat numbers have exploded due to unusually dry conditions and threaten more than 5,5 million hectares of grasslands, the report said.

In one of the areas where the foxes have been released, rat numbers have dropped 70%, it added.

“The silver fox was chosen to be the rat fighter for its distinctive ability to run, hunt and live under the harsh living conditions on the prairie,” Ni said.

Silver foxes are more normally bred in Xinjiang for their rich fur, used to make clothing.

Other parts of Xinjiang are using wolves, eagles and even chickens and ducks to control rat numbers, Xinhua said.

“It is a green way to tackle the rat problem,” added another official, Lin Jun.