French authorities say they want to move up to 1,000 migrants living in the notorious Jungle camp in the port town of Calais.
Government representative Fabienne Buccio said they would be given a week to take up shelter offered elsewhere.
"The time has come to move on, no-one must live in the southern part of the camp, everyone must leave this section," Ms Buccio said.
Officials would visit the camp on Monday to explain the plan, she said.
Some 4,000 migrants, most of them from North Africa, the Middle East and Afghanistan, live in the makeshift camp from where they launch often desperate efforts to reach Britain across the Channel.
Their presence has become a highly controversial issue in both France and Britain.
As winter set in, a new centre of 125 converted shipping containers was set up to house 1,500 migrants in better conditions, including heating and sockets for electricity.
But many have been opposed to moving into the containers - which required their palm prints to be taken to move in and out - fearing it could impede their efforts to win asylum in Britain.
Bulldozers were taken into the camp last month to begin clearing part of it away. Riot police oversaw the demolition, which went largely without incident.
French and British officials want to reduce the number of migrants in Calais and deter others from arriving in the hope of reaching the UK.