"If they move to farmland losses will be large. Yemen does not have the capacity to deal with the locusts and has asked the FAO (the United Nations Food and Agriculture Organisation) for helicopters to spray locust-infested areas."

The FAO says the locust swarm in Yemen is the worst since 1993 and only intensive spraying from the air will stop them breeding and causing serious damage to food crops.

Fareih said the locusts were swarming in the eastern provinces of Hadramout, Shabwa and parts of Mahara. The FAO has warned agricultural crops in Wadi Hadramout and other areas including the Sanaa highlands could be at risk.

Yemen, on the southern tip of the Arabian Peninsula, is one of the poorest countries outside of Africa and malnutrition is widespread. The country imports most of its food, so while the locusts threaten the livelihoods of poor farmers, damage to crops would not lead to famine, officials say.

An adult desert locust can eat roughly its own weight in fresh food per day, about two grams.

FAO spokesman Erwin Northoff said Yemen's government with the support of the food agency and international donors would start an aerial control campaign in the second half of July using two helicopters.

The Locust Monitoring and Combating Centre began spraying locusts in May but its cars can only cover small areas. The FAO said the centre lacked equipment, pesticides and trained teams while heavy rain in March and June had helped the locusts breed.