CALAIS, France (AFP) - Unaccompanied migrant children from the Calais "Jungle" camp on Saturday (Oct 15) began arriving in Britain, French authorities said.

The Calais prefecture confirmed that two dozen unaccompanied minors were already bound for a new life in Britain, where they had family members.

"Five Syrian minors and one Afghan minor have just been transferred to the United Kingdom. From Monday, a dozen more minors will follow, then on Tuesday, a dozen more," a spokesman told AFP.

He added there was "no deal for a larger-scale plan" to dispatch more of the 1,300 minors in the "Jungle", according to figures from French NGO France Terre.

The children have been living in squalid conditions in the Calais encampment where charities estimate up to 10,000 migrants from Africa, the Middle East and Asia have settled in the hope of reaching Britain. The camp faces demolition.

Saturday also saw the start of construction on a new wall designed to block migrant access to the Calais port, a magnet for would-be stowaways who target British-bound lorries.

The first 4m-high concrete panels in the so-called "anti-intrusion" wall were moved into place, according to an AFP reporter at the scene.

When complete, the wall will stretch for around a kilometre and add to some 30km of existing wire fences along the road leading to the port.

"Work is being undertaken on schedule and should be finished by the year's end," said the Calais prefecture spokesman of the €2.7 million (S$4.1 million) structure, which Britain has agreed to finance.

The "Jungle" has become a symbol of the Europe's biggest migrant crisis since the World War II and a major source of Anglo-French tension, leading President Francois Hollande to demand that the site be demolished before the end of 2016.

The French government has yet to give an official date for dismantling the camp.

Initial indications that it might happen as early as this Tuesday, however, proved premature and the plan has been put back at least a week, sources indicated.

Meanwhile work has been stepped up on the creation of reception centres across France to house as many as 9,000 people from Calais.

On Friday, around 200 people demonstrated at Croisilles, about an hour inland from Calais, against the proposed creation of a migrant reception centre for up to 60 people once the Jungle actually closes, a prefecture source said on Saturday.

The source said the rally, which the local mayor said was organised by locals but had attracted a number of far-right National Front supporters, passed off without incident.

In a further development Saturday, 50 lawyers arrived at the camp to provide the migrants with advice so they could fill in forms and be "aware of and assert their rights", Flor Tercero, head of an association of lawyers for foreigners' rights, told AFP.

"We are well aware that the 'Jungle' is a place where living conditions are undignified and inhuman and that cannot go on," Tercero said.

Away from Calais, a French fishing boat earlier on Saturday came to the aid of four migrants who ran into difficulties in the English Channel as they made for England in a makeshift vessel, local authorities said.

The fishing boat rescued the group, all four of whom were suffering from hypothermia, and handed them over to police.