French demolition workers set about razing makeshift shelters in the "Jungle" migrant camp for a third day on Wednesday under close watch of dozens of police officers equipped with water cannon. The destruction of the southern half of the sprawling shantytown in the northern port city of Calais, where thousands of migrants and refugees have gathered in the hope of finding passage to England, has sparked often violent resistance from residents. "You need to get out, the demolition is starting," police warned, banging on the side of the shacks in what has become France's biggest slum, as a bulldozer stood by. Smouldering piles marked places where several shelters were burned down overnight, though no-one knows how the fires were started. On Monday, residents clashed with riot police as destruction of the camp began. France wants the migrants, mostly fleeing war and poverty in the Middle East and North Africa, to move into better accommodation and reception centres. However, Jungle residents fear moving would take them further away from their goal of reaching Britain and restrict their movement. Officials say the demolition will affect between 800 and 1,000 people, although charities working there say there are more than 3,450 people in the southern half of the camp, including 300 unaccompanied children. Charity workers say some migrants carrying backpacks left the camp overnight. "Who knows where they are going. It's impossible to know the level of fear and uncertainty they are experiencing at this point," said Tom Radcliffe of Help Refugees. Some may have been heading for other camps along the northern French coast — at Dunkirk or Tetenghem, where conditions are even worse than those in the Jungle. Belgium on Monday turned back more than 600 migrants trying to enter its territory to reach Zeebrugge port, another launching pad for reaching Britain. Police also began checking IDs at the entrance to the camp. "They were just trying to intimidate us. They weren't even really looking at our passports," said one young activist from Britain who, like others in her group, were unwilling to give her name or affiliation.