Mauritania has appealed for urgent international aid to combat swarms of locusts entering the country.
A locust swarm can devour as much food as 1,000 people
Large numbers have been moving from their spring breeding areas in north-west Africa towards Mauritania, Senegal and Mali.
They could be the worst swarms in 15 years, the UN Food and Agriculture Organisation says.
Mauritania says seven regions have been hit, and it has proposed a $5m programme to treat the affected areas.
Rural Development Minister Ahmedou Ould Ahmedou submitted a plan to treat some 3,000 square kilometres but said this could be a conservative estimate.
The FAO issued its first warning of a coming locust plague back in February, when unusually high rates of breeding were detected south of the Atlas Mountains in Morocco and Algeria.
Major insecticide spraying programmes were initiated, some funded by western donors, aiming to cut the plague off at source.
Summer rains have started in the area, which means the insects will lay more eggs as they travel.
Swarms could eventually reach the Darfur region of Sudan, where conflict has already created a major humanitarian crisis.
Locusts can eat their own weight in food every day, which means a single swarm can consume as much food as several thousand people.