The worst locust outbreak that parts of East Africa have seen in 70 years needs some $76 million to help control and the money is “required by, actually, now,” the United Nations has said.

So far just $15 million (£12m) has been mobilised to help stop the outbreak that threatens to worsen an already poor hunger situation for millions of people in Kenya, Ethiopia, Somalia and elsewhere, Dominique Bourgeon, emergencies director with the UN Food and Agriculture Organisation (FAO), told a briefing in Rome.

“You can imagine that a country that has not seen such a thing in 70 years is not well prepared,” he said of Kenya, East Africa's economic hub.

The outbreak, blamed in part on a changing climate, now threatens to spread to South Sudan and Uganda and new rains in the weeks to come will fuel fresh vegetation and a new wave of breeding. The outbreak might not be under control until June when drier weather arrives, authorities have said.

But by then the number of locusts, if left unchecked, could grow 500 times, experts have warned.

Locust swarms threaten catastrophe for farmers in East Africa Show all 14 1 /14 Locust swarms threaten catastrophe for farmers in East Africa Locust swarms threaten catastrophe for farmers in East Africa Local farmer Theophilus Mwendwa runs through a swarm of desert locusts to chase them away in Kitui County, Kenya EPA Locust swarms threaten catastrophe for farmers in East Africa A farmer's son walks through a swarm of locusts in Kitui County, Kenya AP Locust swarms threaten catastrophe for farmers in East Africa Locusts swarm on a highway at Lerata village in Kenya AFP/Getty Locust swarms threaten catastrophe for farmers in East Africa Local farmer Theophilus Mwendwa runs through a swarm of desert locusts to chase them away in Kitui County, Kenya EPA Locust swarms threaten catastrophe for farmers in East Africa Local farmer Theophilus Mwendwa runs through a swarm of desert locusts to chase them away in Kitui County, Kenya EPA Locust swarms threaten catastrophe for farmers in East Africa A man chases away a swarm of desert locusts in Kitui County, Kenya EPA Locust swarms threaten catastrophe for farmers in East Africa A farmer walks among a swarm of locusts on grazing land in Galmudug region, Somalia Reuters Locust swarms threaten catastrophe for farmers in East Africa Somali farmers on Saturday urged their government and the international community to help protect their crops from an invasion of locusts that is leaving many unable to feed their families Reuters Locust swarms threaten catastrophe for farmers in East Africa A desert locust plucked from the swarm on farmland in Galmudug region, Somalia Reuters Locust swarms threaten catastrophe for farmers in East Africa The insects have already destroyed 175,000 acres of farmland in Somalia and neighbouring Ethiopia, threatening food supplies in both countries in the worst locust invasion in 70 years, the Food and Agriculture Organisation said on Wednesday Reuters Locust swarms threaten catastrophe for farmers in East Africa A farmer lifts a ketle among a swarm of locusts on grazing land in Galmudug region, Somalia Reuters Locust swarms threaten catastrophe for farmers in East Africa Farmers lift a plastic sheeting to fend off a swarm of locusts on grazing land in Galmudug region, Somalia Reuters Locust swarms threaten catastrophe for farmers in East Africa Boys attempt to fend off a swarm of locusts on farmland in Galmudug region, Somalia Reuters Locust swarms threaten catastrophe for farmers in East Africa Farmers watch on as swarm of locusts descends on grazing land in Galmudug region, Somalia Reuters

“If after April the money has come, it's somehow useless,” FAO chief Qu Dongyu told the briefing. “So the timing, location, is crucial.”

Already the locusts, moving in swarms of hundreds of millions, have stripped some crops bare. An Ethiopian representative at the briefing told the FAO that some farmers in Africa's second most populous nation have lost 90% of their production.

The locusts have been moving steadily towards Ethiopia's Rift Valley, the country's breadbasket, the UN says.

Authorities have said aerial pesticide spraying is the only effective control in the outbreak, but officials in Kenya and elsewhere have said more planes and more pesticide are needed.

A single swarm can contain up to 150 million locusts per square kilometre of farmland, an area the size of almost 250 football fields, regional authorities say. One especially large swarm in northeastern Kenya measured 60 kilometers long by 40 kilometers wide (37 miles long by 25 miles wide).

“We depend a lot on this season and we worry that the locusts will destroy our harvest and we end up remaining hungry through the rest of the year, waiting for October for the next cropping season,” one farmer in Kenya's Kitui county, Esther Kithuka, has told the FAO.

Even before this outbreak, nearly 20 million people faced high levels of food insecurity across the East African region long challenged by periodic droughts and floods.