It would create a food crisis, Dominique Burgeon, director of emergencies for the UN Food and Agriculture Organisation (FAO), told the BBC.
Tanzania, Ethiopia, Somalia, Kenya and Uganda are affected, according to the UN official. Efforts to control the infestation have so far not been effective.
Aerial spraying of pesticides is the most effective way of fighting the swarms but countries in the region do not have the right resources, the director said in his remarks.
The government said recently that it had hired three spray planes in preparation to possible invasion of desert locusts before the pests were reportedly spotted in parts of Kilimanjaro region—reports that were refuted by authorities.
Agriculture minister Japhet Hasunga said two planes were to come from the Desert Locust Control Organisation for Eastern Africa (DLCO-EA) based in Addis Ababa, and one from the International Red Locust Control Organization for Central and Southern Africa (IRLCO-CSA) in Lusaka.
He said the ministry had already applied for a license from the Tanzania Civil Aviation Authority (TCAA) to deliver the planes to Tanzania.
There are fears that the locusts - already in their billions - will multiply further.
The FAO said last month that the insects are breeding so fast that numbers could grow 500 times by June.
The UN body has now called on the international community to provide nearly $76m (£58m) to fund the spraying of affected areas with insecticide.
"If it doesn't, the situation will deteriorate and then you will need to provide massive food assistance for a humanitarian situation that may even get out of control," Burgeon said.
The locust invasion is the worst infestation in Kenya for 70 years and the worst in Somalia and Ethiopia for 25 years.
Somalia has declared a national emergency in response to the crisis, while the Ethiopian government has called for "immediate action" to deal with the problem affecting four of the country's nine semi-autonomous regions.
Kenya has deployed aircrafts to spray pesticides in several regions, while Uganda plans to send soldiers to northern regions to spray affected areas.
The locusts are thought to have spread from Yemen three months ago, reports indicated.