Most of the migrants seek to enter the UK
French police have closed down a makeshift shelter for illegal migrants in Calais a day after it was opened.
The disused warehouse in the northern port was being used by about 100 migrants, mostly from Afghanistan.
The building was rented by an activist group, which turned it into a camp in defiance of a ban on giving shelter to illegal immigrants in the town.
Calais attracts migrants aiming to get into the UK. In September, a makeshift camp known as "the jungle" was closed.
The move was criticised by human rights groups, who argued that many migrants should be treated like refugees.
A local campaign group, No Border, took over the warehouse not far from the port on Saturday with the aim of turning it into a permanent shelter for migrants.
The authorities say camps like 'the jungle' encourage human trafficking
But on Sunday morning, police put up a security cordon around the building, allowing those inside to leave in search of food but not to return.
Eventually, there were only a few migrants and activists remaining in the warehouse when police moved in during the afternoon.
"They forced their way in. There are no more migrants inside," Helene, an activist from No Border, told the AFP news agency.
Calais Mayor Natacha Bouchart had said she was ready to sign an eviction order to quickly get the migrants out and not "allow zealots to manipulate us and risk triggering an extreme response".
French Immigration Minister Eric Besson made it clear he would not allow the re-establishment of a "new jungle" in or around Calais, because it might "serve as a rear base for human trafficking rings".
But the BBC's Hugh Schofield in Paris says the question of how to deal with migrants' humanitarian needs, especially during winter, has still not been resolved.
Makeshift, insanitary camps such as "the jungle" sprang up after French officials closed the Red Cross centre at Sangatte in 2002.