Afghan authorities are examining the extent of an unprecedented locust infestation that has prompted local officials in some areas to offer wheat as a reward to residents for killing the insects.

Some 300 tonnes of locusts have been killed by people in the northwestern province of Badghis alone in recent weeks, Abdul Ghafar Ahmadi, a senior official from the agriculture ministry, said on Saturday, citing provincial officials.

Local officials in Badghis and neighbouring Herat have promised residents seven kilos of wheat in return for killing one kilo of locusts, amid a global surge in food prices that has hit Afghanistan hard, Mr Ahmadi said.

"The infestation of locusts has been unprecedented in Afghanistan. It is pretty bad here in Badghis which is also suffering from drought," he told Reuters from Badghis.

"I have heard from local officials that residents have killed 300 metric tonnes of locusts."

He could not say how many hectares of cultivated land had been destroyed by the infestation, but said a mechanical campaign to kill the insects has been going in several parts of the region, which border Turkmenistan.

"This is a regional problem and is not limited only to Afghanistan," he said.