( CNN ) -- Police in northern France moved in Wednesday on makeshift migrant camps near the port of Calais , prompting a standoff with the defiant residents -- many of whom have fled conflicts in Syria , Sudan and Eritrea . By late afternoon , a CNN producer observed that the migrants ' tents had all been destroyed . One activist told CNN police were responsible . About a dozen police officers remained , along with 50 to 60 migrants who did n't know where to go . A local prefect reportedly told the migrants they can stay at the camp until Thursday . But Thursday is Ascension Day , a public holiday , so it 's not clear if the migrants will be cleared out before Friday . Hundreds of migrants had gathered in the ramshackle camps , some seeking to claim asylum in France and others hoping to find a way to reach British soil . Mattheu Adt of international humanitarian organization Medecins du Monde , told CNN from one of the camps that police had asked the migrants to move to an undisclosed location , but that the migrants were refusing . Authorities also asked the migrants to shower and decontaminate their clothes , amid concern over an outbreak of the contagious skin condition , scabies , he said . Migrants refused to do that , Adt said , because of concerns their tattered tents would be gone when they returned . `` They fear they will be arrested at the showers , '' said CÃ©cile Bossy , an activist with Medecins du Monde . She said migrants were given scabies medication Tuesday night but did n't understand what it was for . Adt said the makeshift camp where he is located housed about 600 people , roughly half of them Syrian , and between 200 and 300 Eritrean and Sudanese . A spokesman for the charity Secours Catholique in Calais confirmed that police had arrived at about 6:30 a.m. local time at a camp and asked the migrants there to board buses to go to `` decontamination '' areas . Many of the migrants refused , he said . Earlier , police destroyed another camp -- which housed about 300 people -- with bulldozers , he said . The migrants have been involved in discussions with authorities but do n't know where to go , he said . Official : Dismantling under way . An official in Calais told CNN that authorities planned to dismantle the migrants ' makeshift camps by the end of Thursday . Roughly 550 migrants lived in those camps , said Georges Bos , the associate chief of staff of the Pas-de-Calais prefecture -- the local branch of the French government . `` By tonight there will be no possibility left to go to these camps , '' he said . Bos said authorities had offered to take the migrants by bus to places where they could shower , adding that dismantling the camps was necessary to prevent further spread of scabies . He said that the prefect of the Pas-de-Calais region had told migrants their immigration status would not be checked and that no arrests would be made . It 's not the first time French authorities have sought to move on the migrants who congregate in the area around Calais , many hoping to smuggle themselves into Britain inside freight trucks going across the English Channel . A camp in Sangatte was dismantled in 2002 and another known as the Jungle was broken up in 2009 . But after each clearance effort , new makeshift camps spring up . 'Deafening silence ' Medecins du Monde is one of a number of humanitarian and rights groups that signed an open letter to French Prime Minister Manuel Valls on Tuesday voicing concern over the plight of the migrants . `` The situation in Calais is worsening in a deafening silence , '' it said . `` About 700 foreigners , for the most part of Syrian , Afghan and Eritrean origin , fleeing conflicts , violence and persecution , are installed in the town . '' About 550 of those migrants are living in makeshift camps , the letter said , having claimed asylum in France or waiting to attempt the crossing to Britain . `` They live in catastrophic sanitary conditions which have encouraged the development of a scabies epidemic . '' The groups were `` stunned '' last week to learn that authorities planned to clear the camps and tackle the scabies outbreak on Wednesday , the letter said -- without coming up with any alternative place of shelter for the large majority of people concerned . `` We can anticipate the effects of this expulsion ... inappropriate medical care , people wandering on the streets of Calais , daily police checks , violence , despair and the taking of growing risks to attempt a passage to the United Kingdom , which , since the start of the year , have already caused the deaths of several exiles , '' it said . The groups urge the French government to come up with a plan to tackle the sanitary situation in the camps while living up to its responsibility to protect the migrants on its soil . The letter was also sent to the French interior minister and the minister for health and social affairs . Would-be immigrants storm Spanish enclave on Moroccan coast . Italy 's Navy rescues 6,000 migrants in just four days . The deadliest trek : Dying in the desert . CNN 's Stephanie Halasz and journalist Bastien Inzaurralde contributed to this report .
NEW : Camps appear dismantled , but about 50 to 60 migrants remain at one . Police are trying to shift migrants from makeshift camps near Calais . The migrants do n't want to leave , wo n't take steps to tackle a scabies outbreak , authorities say . Calais is a magnet for migrants seeking to reach Britain or claim asylum in France .