French CRS riot police watch as smoke and flames billow from a burning makeshift shelter during a protest by migrants against the partial dismantlement of the camp for migrants called the "jungle", in Calais, northern France, February 29, 2016. [Photo/Agencies]

"The migrants are just going to run and hide in the woods and the police are going to have to go after them," said activist Francois Guennoc of the Auberge des Migrants migrant support group.

Regional Prefect Fabienne Buccio had said the police presence was needed because "extremists" could try to intimidate migrants into turning down housing offers or buses to reception centres.

Interior Minister Bernard Cazeneuve said last week that authorities would work with humanitarian organisations to relocate the migrants to a nearby park of converted shipping containers or other reception centres around France.