Crops in north Africa are under threat from swarms of locusts, says the UN Food and Agriculture Organization.
Swarms can devour fields of crops in a few minutes
Outbreaks of locusts have been reported in Mauritania, Niger and Sudan and observers fear they could spread across the northern half of the continent.
Affected governments and international donors have been alerted.
"The situation has the potential to develop rapidly and it could be a matter of weeks," said the FAO's Locust Group in a statement.
"We must immediately boost the number of surveys, the level of monitoring and prepare for expanded intervention."
They said there were five survey teams operating in north-western Mauritania, including two with pesticide-spraying capabilities.
Five aircraft are on standby in north-eastern Sudan where mature adult locust swarms have been seen laying eggs along the Atbara river.
In northern Niger, locusts have been reported at a density of 20 hoppers per square metre.
"The number of locusts is increasing rapidly. They are beginning to concentrate themselves into groups characteristic of an outbreak," said the Locust Group.
"If the situation worsens this migratory pest may move northwards across northern Mauritania into Morocco, from Sudan towards the Red Sea and from Mali and Niger into Southern Algeria."
Desert locusts are normally solitary insects but when climatic conditions are favourable they can rapidly increase in number.
When they group, the young, wingless locusts - known as hoppers - march together in search of food.
As adult, winged insects they form swarms that can travel in tens of millions and travel great distances, crossing international borders in search of food.
They can devastate crops within minutes.
A major locust plague in 1987 to 1989 originated in western Sudan and spread as far as India.
The UN organisation says a full-fledged desert locust plague has the potential of damaging the livelihood of a tenth of the world's population.