It says harvests in Ethiopia, Somalia and Kenya are all under threat.

WFP says the crisis is likely to be compounded by an infestation of caterpillars, known as army worms.

A million people need food in Ethiopia (UN photo)

They have already destroyed large swathes of crops in Kenya and are expected to invade Ethiopia and Somalia as well.

In Ethiopia, river beds which can normally only be crossed by boat are now completely dry, and are being used by children as make-shift football pitches.

In the province of Wollo - the centre of the Ethiopian famine of 1984 - WFP says some villages have been deserted by their inhabitants, as they search for food.

Emergency appeal

Most crops have been impossible to grow, and people have now sold all they can to survive.

Last week, WFP appealed for $40 million to help it pay for an emergency operation to feed over a million people in eight regions of Ethiopia.

Somalia and Kenya are also facing major food shortages.

WFP says disturbingly high levels of malnutrition have been reported in north-eastern Kenya, with the number of malnourished children doubling to nearly 40% since the beginning of the year.

In neighbouring Somalia, livestock have been dying of thirst, while fighting has hampered the delivery of emergency aid.