The insects are devouring crops with Kenya one of the worst affected
Unusual climate conditions are partially to blame for the plague, which is posing an unprecedented threat to food security in some of the world's most vulnerable countries.
The insects are devouring crops, with Kenya one of the worst countries to be affected.
One swarm measured 60km (37 miles) by 40km (25 miles) in the country's northeast.
A spokesman for the country's Intergovernmental Authority on Development (IGAD) said: "A typical desert locust swarm can contain up to 150 million locusts per square kilometre.
"Swarms migrate with the wind and can cover 100 to 150 kilometres in a day.
"An average swarm can destroy as much food crops in a day as is sufficient to feed 2,500 people."
The outbreak of desert locusts, considered the most dangerous locust species, has also affected parts of Somalia, Ethiopia, Sudan, Djibouti and Eritrea, and IGAD warns that parts of South Sudan and Uganda could be next.
The outbreak is making the region's food crisis worse, the UN Food and Agriculture Organisation (FAO) has warned.
Hundreds of thousands of acres of crops have been destroyed.
The further increase in locust swarms could last until June as favourable breeding conditions continue, IGAD said, helped along by unusually heavy flooding in parts of the region in recent weeks.
Major outbreaks can be devastating. A major one between 2003 and 2005 cost more than $500m (£384m) to control across 20 countries in northern Africa, the FAO has said, with more than $2.5bn (£1.9bn) in harvest losses.
To help prevent and control outbreaks, authorities analyse satellite images, stockpile pesticides and conduct aerial spraying.
In Ethiopia, officials said they have deployed four small planes to help fight the invasion.
Comment: At least 360 000 ha (890 000 acres) of crops have been affected in Rajasthan, northern India which is currently in the midst of the state's worst locust infestation in 60 years.
Locust outbreaks from last year include: