The Kazakh government, which has come under strong criticism for failing to respond to the growing swarm, has brought in emergency supplies of pesticides and ordered the streets to be sprayed by teams of men on foot at night.

The locusts have infested up to seven million hectares of land in Kazakhstan.

Correspondents say that Kazakh residents speak of a dense carpet of locusts covering streets and buildings and invading houses and shops.

For weeks, the plague of locusts has been advancing like a moving carpet from the north, devouring crops and vegetation.

The insects are also spreading across Russia at the rate of 50 kilometres (30 miles) a day, where they are destroying large areas of crops.

And they have travelled south, infesting some 300,000 hectares of land in neighbouring Uzbekistan.

Locust headache

People in some areas of Kazakhstan speak of locusts crunching underfoot. The BBC's Central Asia correspondent Louise Hidalgo says that an onslaught like this has not been seen for decades.

Pedestrians are having to dance around the locusts

In the capital, Astana, they completely cover the facades of some buildings and have clogged up car engines.

"Local motorists have a headache: the locusts swarm into car radiators, and the cars' exteriors, covered with crushed insects, are a pitiful sight," the Russian news agency Itar-tass reported

The locust problem has been increasing steadily in Kazakhstan since the break-up of the Soviet Union.

The Kazakh authorities have appealed for help from foreign donors.