The immigrants had sneaked on to the truck at the French port of Calais and were probably trying to travel on to Britain. But the truck, carrying fruit, had entered France from Britain.
It was the immigrants themselves who, suffering from the cold, rapped on the walls of the truck to alert the driver as he waited at a motorway toll station, officials said.
Rights groups say there has been a sharp rise in the number of illegal immigrants in the region around Calais, particularly from Afghanistan, Congo and Sudan.
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