Medics in France had to treat migrants hidden in a UK-bound refrigerated lorry for hypothermia on Saturday, after the driver heard their cries for help, officials told AFP.

The driver heard the group of 15 stowed away in his lorry while at a motorway rest stop, a senior official with the Pas-de-Calais prefecture in northern France said.

"Their state of hypothermia suggests that they had been there for several hours," Christian Vedelago, head of the local prefect's office, said.

Four of the migrants had to be hospitalised and another four were declared minors and handed over to the care of an association, he added. The group, which is reported to be from Eritrea, also included one woman.

Perilous attempts to reach the UK

Several of those rescued had already received official orders telling them to leave France.

The Moroccan lorry driver, who was transporting frozen vegetables, was not under investigation, Vedelago said.

Despite extensive security checks at the ports in northern France where ferries leave for Britain, and at the cross-Channel tunnel, migrants still try to board lorries bound for England, even if the preferred route is now to cross the sea in small boats.