A member of that delegation later cast doubt on the duck deployment. Zhang Long, a professor from China Agriculture University said ducks would not be suited to Pakistan.

"Ducks rely on water, but in Pakistan's desert areas, the temperature is very high," he said.

A swarm of desert locusts is one of the animal kingdom's most awesome spectacles. The groups can be hundreds of square miles in size and contain billions of insects. The marauders can fly up to 90 miles per day and if good rains fall and conditions are favourable, can increase their numbers 20-fold in three months. Almost all crops and non-crop plants are vulnerable and the insects are one of the biggest threats to food security in large parts of the world.

Any Pakistan deployment would not be the first time China has used ducks to combat locusts.

In 2000, an army of 700,000 specially trained ducks and chickens was mobilised to help fight China's biggest locust plague in 25 years.

The ducks deployed to Xinjiang had been trained to pursue and eat locusts at the sound of a whistle.

Ducks were chosen after farmers first noticed that chickens were fond of locusts. Experiments with waterfowl found ducks ate twice as many and were less prone to being eaten by predators.

China has already announced this year it is sending ducks to Xinjiang in case the locusts spread from Central Asia.

United Nations experts last night told the Telegraph that even the hungriest ducks would be overwhelmed by the size of the swarms.

Keith Cressman, senior locust forecaster for the UN's at Food and Agriculture Organisation said: “There are not enough ducks and they cannot eat enough desert locusts to have a significant impact.”

It is also not clear what would happen to the masses of ducks once they had eaten the locusts. Duck meat is halal, but not widely eaten in Pakistan.

Imran Khan earlier this month declared a national emergency in Pakistan because of the threat to agriculture.

"We are facing the worst locust infestation in more than two decades and have decided to declare national emergency to deal with the threat," information minister Firdous Ashiq Awan said at the time.

Swarms have been spreading through countries from eastern Africa to South Asia, destroying crops and pastures. The infestation, together with unseasonal rain and a scourge of low quality seeds, has hit major crops in Pakistan’s largest producing regions, weighing on its already fragile economy. And it has also migrated into India.