Radio reports from the region, which is squeezed between Nigeria to the west and Chad to the east, said locusts darkened the skies and ate any green leaves they could find.

Last year, locusts munched their way across swathes of West Africa in the worst infestation in 15 years. The invasion raised fears of famine in a region where many are subsistence farmers.

Arid, semi-desert Niger and Mauritania were among the hardest hit. On Thursday, the United Nations said drought and the locust infestation had left 3.6 million people in critical need of food aid in Niger.

Cameroon, which stretches from mangrove swamps on the Atlantic Coast to the more arid north by Lake Chad, was not affected by last year's plague.

Tchatat said a light aircraft from the Aerial Pest Control Unit was in the Far North to find out where the locusts came from and where they were reproducing. Some 7,000 litres of pesticides are available in the region to combat the insects.

Tchatat said in March the Far North faced food shortages because of low rainfall coupled with the advancing desert and the destruction of crops by migratory birds and elephants.

Some 2,000 tonnes of cereals have been provided for the local populations.

Millions of hectares of land in West Africa have been sprayed with pesticides to prevent another locust attack. On Tuesday, U.N. officials said West Africa had cut the risk of another plague but warned there was no room for complacency.