Zambia has ordered the national air force into action to fight a plague of pests that has invaded maize crops and threatened vital food supplies.

The air force is transporting pesticides across the country so that fields can be sprayed in an attempt to combat infestations of "army worms", a type of larvae moth that can decimate crops.

"The Zambia Air Force has since begun to airlift chemicals," President Edward Lungu's spokesman said in statement.

"The president has directed that the chemicals that were purchased under emergency operations should be distributed to all parts of the country."

Agriculture ministry permanent secretary Julius Shawa told reporters that army worms had damaged crops in four of the country's ten provinces -- Copperbelt, Luapula, Central and Lusaka.

"It is not the entire province. It's only some districts in the four provinces," said Shawa.

Lungu's spokesman said the president was concerned that harvest volumes would be badly damaged "if the outbreak of the worms is not controlled speedily."

No details were available on the number of aircraft involved in the operation.

Maize -- or corn -- is a stable crop across much of Africa, used to make dishes such as pap.