A locust plague of almost biblical proportions is ravaging Eastern Africa's food bowl, prompting the United Nations to call for international help.

Key points: Climate change is thought to have contributed to "exceptional" breeding conditions

Climate change is thought to have contributed to "exceptional" breeding conditions Even a small swarm of locusts can consume food for 35,000 people in one day

Even a small swarm of locusts can consume food for 35,000 people in one day The UN warns the desert locusts may spread to the Middle East and south Asia

Hundreds of millions of the bugs have swarmed into Kenya from Somalia and Ethiopia, creating the worst outbreak of desert locusts there in 70 years.

Somalia and Ethiopia have not had an infestation like this in a quarter of a century. It has destroyed farmland and threatened an already vulnerable region with devastating hunger.

The UN Food and Agricultural Organisation (FAO) has warned the "unprecedented size and destructive potential" of the swarms could leave millions of people without food.

A girl waves her shawl to try to chase locusts away from her family's crops in Kitui county, Kenya. ( AP: Ben Curtis )

"Even cows are wondering what is happening," Ndunda Makanga, a Kenyan farmer, said.

"Corn, sorghum, cowpeas, they have eaten everything."

The rose-coloured locusts turn whole trees pink, clinging to branches like quivering ornaments before taking off in hungry, rustling clouds.

Even small swarms can have a devastating impact on food production. ( AP: Ben Curtis )

When rains arrive in March and bring new vegetation across much of the region, the numbers of the fast-breeding locusts could grow 500 times before drier weather in June curbs their spread, the FAO warned.

"We must act immediately," The FAO's David Phiri said.

About US$70 million ($103 million) is needed to increase aerial pesticide spraying, the only effective way to combat them, the UN says.

Last week, Peter Munya, a Kenyan cabinet secretary in the Ministry of Agriculture, confirmed the country was deploying three more pesticide spray aircraft to spray some 20,000 litres of the liquid.

Speaking on Friday, Mr Munya told local broadcaster Citizen TV that 10 counties were affected, but most of the country's breadbasket was unaffected — except for the south-eastern Kitui county.

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Situation now of 'international dimensions'

In a press release issued on Monday, FAO director-general Qu Dongyu said the agency was activating fast-track mechanisms to support governments, warning the situation was now of "international dimensions".

"Authorities in the region have already jump-started control activities, but in view of the scale and urgency of the threat, additional financial backing from the international donor community is needed so they can access the tools and resources required to get the job done," Mr Qu said.

Even before the locusts, some 20 million people in the region faced food insecurity. ( AP: Ben Curtis )

That will not be easy, especially in Somalia, where parts of the country are in the grip of the al Qaeda-linked al Shabaab extremist group.

Even a small swarm of the insects can consume enough food for 35,000 people in a single day, Jens Laerke of the UN humanitarian office in Geneva, said.

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About 70,000 hectares of land in Kenya are already infested.

"This is huge," Kipkoech Tale, a migratory pest control specialist with the Kenyan agriculture ministry, said.

"I'm talking about over 20 swarms that we have sprayed. We still have more. And more are coming."

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 Kenya's north-east measured 60km long and 40km wide.

Kenya needs more spraying equipment to supplement the four planes now flying, Mr Tale said. Ethiopia also has four.

They also need a steady supply of pesticides, Francis Kitoo, deputy director of agriculture in Kitui county, said.

'The locals are really scared'

These two Samburu men work for a county disaster team identifying the location of the locusts, pictured in Samburu county, Kenya. ( AP: Patrick Ngugi )

"The locals are really scared because they can consume everything," Mr Kitoo said.

"I've never seen such a big number."

A changing climate had contributed to "exceptional" breeding conditions, Nairobi-based climate scientist Abubakr Salih Babiker, said.

Migrating with the wind, the locusts can cover up to 150km in a single day.

They are now heading toward Uganda and fragile South Sudan, where almost half the country faces hunger as it emerges from civil war.

Uganda has not had such an outbreak since the 1960s and is already on alert.

The locusts also are moving steadily toward Ethiopia's Rift Valley, the breadbasket for Africa's second-most populous country, according to the UN.

"The situation is very bad but farmers are fighting it in the traditional way," Buni Orissa, a resident of Ethiopia's Sidama region, said.

A boy tries to chases the pests away from his family's crops. ( AP: Ben Curtis )

"The locusts love cabbage and beans. This may threaten the shaky food security in the region."

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

Numerous desert locust swarms have also been breeding in India, Iran and Pakistan since mid-2019.

The FAO said locust breeding in Egypt, Eritrea, Saudi Arabia, Sudan and Yemen could also see swarms expand in the coming months.

AP/ABC