Calais (France) (AFP) - Workers ramped up demolition of France's notorious Calais "Jungle" on Wednesday after fierce blazes cut through a swathe of the camp overnight, sending migrants fleeing for safety.

Wearing hardhats and orange overalls in the morning fog, a team of around 15 workers resumed tearing down tents and makeshift shelters at the camp that has become a symbol of Europe's migrant crisis.

In the distance, a new fire threw black smoke into the sky as several dozen wood shacks smouldered on a main thoroughfare of the sprawling slum.

"Someone burned our tents. Maybe they used petrol or something, I don't know, but the fires spread fast. We had to run out in the middle of the night," said Arman Khan, a 17-year-old Afghan.

"I left all my things behind, I have nothing now."

Riot police had cordoned off the demolition area while aid workers and government officials checked that the dwellings were empty.

Others carted away the debris and abandoned belongings -- mattresses, multi-coloured blankets, supermarket trollies and so on -- in small earth-movers.

Gas canisters, sinks, refrigerators and other metal objects lay scattered across the desolate scene.

The fires spread just hours after workers moved in Tuesday to clear the squalid camp that has been home to an estimated 6,000-8,000 migrants, many with hopes of reaching Britain.

A Syrian man was taken to hospital with injuries to his eardrums after a gas canister exploded in the flames.

A local official played down the blazes, telling AFP: "It's a tradition among communities who set fire to their homes before leaving."

Located next to the port of Calais, the Jungle has for years been a launchpad for migrants attempting to make it to Britain by sneaking onto lorries or jumping onto trains heading across the Channel.

Since Monday, 3,242 adults have been transferred to centres around France and 772 unaccompanied minors have been moved to shipping containers converted into temporary shelters in the Jungle, the interior ministry said.

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The numbers represent around half the camp's estimated population before the operation began, according to official figures.

The authorities have said those who agree to be moved can seek asylum in France. Those who refuse risk deportation.

The fate of more than 1,000 unaccompanied minors is of particular concern.

- 'It's very scary' -

French Interior Minister Bernard Cazeneuve said Tuesday that all those "with proven family links in Britain" would eventually be transferred and that London had committed to reviewing all other cases where it was "in the child's interest" to settle across the Channel.

British Interior Minister Amber Rudd on Monday pledged to bring eligible children from France to Britain "as quickly and as safely as possible", without specifying numbers.

The head of Save the Children on Tuesday called for a smooth process to ensure their safety.

"It's very scary, I think, for kids particularly. You see them coming in with bulldozers. This is where children have been living for weeks and months in some cases," Carolyn Miles told AFP in New York.

Britain took in around 200 teenagers in the week before the clearance began as an eleventh-hour gesture, with the transfers resuming Tuesday after a hiatus on Monday.

An AFP reporter saw a coach carrying around 30 child refugees arrive at an immigration office in the London district of Croydon.

The curtains on the bus were drawn after pictures of some teenagers reunited with family in Britain sparked accusations that they had lied about being minors.

Back at the Jungle on Wednesday, the line of migrants stretched more than 200 metres (yards) outside the building where the crucial interviews take place.

An Afghan migrant who appeared to be in his late 20s emerged angrily from the hangar. "I'm a minor," he said in halting English. "I'm 17 and they don't respect me. I was pushed out of the minors' line. France is no good!"

Police in Calais have battled near-nightly attempts by migrants to reach Britain over the past year.

The town's Mayor Natacha Bouchart said seeing people queue to leave the camp was "a great relief".

But many locals fear more settlements will sprout up in the area once the Jungle is razed.