The Home Office is removing 600 people every day from a controversial processing centre in Kent amid growing concerns over the mental health of people detained for weeks in cramped and unhygienic conditions. After an outcry at the treatment of asylum seekers at Manston processing centre, the local MP, Roger Gale, has been told by ministers that the total number held within the facility will be cut from 4,100 on Monday to 1,500 by the weekend. A young girl detained at the facility threw a bottle containing a note over the camp’s perimeter fence begging for help on Wednesday. The note compared the facilities to a prison and claimed pregnant women and sick people were being held there. Rishi Sunak said his government was getting to grips with the problems at the Kent centre, but admitted that “not enough” asylum claims are being processed. Gale, the MP for North Thanet who on Monday accused Suella Braverman of deliberately failing to find alternative accommodation for people at Manston, said coaches were now arriving to take migrants away. “Robert Jenrick, the immigration minister, has got a firm grip on this since he visited Manston with me on Sunday. He has already reversed the perverse decision not to find more hotels for the people at Manston. “I’m told that around 600 people were moved out of Manston on Tuesday, and another 600 are due to go today. The figure is supposed to be down to 1,500 by the weekend,” he said. Two coaches with heavily tinted windows were seen leaving the centre at about 4.15pm on Tuesday. It appeared the buses were full of people. The young girl who threw the letter was among a group of children who broke past security guards and ran over to the fence to throw the bottle. The letter was addressed to “journalists, organisations, everyone”. It appeared to suggest 50 families had been held at Manston for more than 30 days. It said: “We are in a difficult life now … we fill like we’re in prison. [sic] “Some of us very sick … ther’s some women’s that are pregnant they don’t do anything for them [sic] “We really need your help. Please help us.” The letter claimed there is a disabled child at the site. “He’s really bad, they don’t even care about him. “It’s not easy for someone who has children … There’s a lot of children they shouldn’t be here. They should be in a school not prison,” it said. The Guardian revealed on Wednesday that the Home Office had bussed asylum seekers from Manston into central London and left them at Victoria railway station without accommodation or warm clothing. The group of 11 people were stranded on Tuesday evening with nowhere to stay, without winter coats, many of them in flip-flops, according to volunteers with the Under One Sky homelessness charity, who provided them with emergency supplies of food and clothes. Kevin Mills, a branch secretary for PCS union which represents border force staff, said his members working at the site have become increasingly concerned over the wellbeing of those held there. “There is a real worry for the mental health and wellbeing of the people held there. Being there in that environment and in those conditions must take its toll. They can see that it is a problem for people who have already been through a lot to get here,” he said. The potentially unlawful conditions at Manston has exposed those working there to legal action by asylum seekers and even criminal investigation. Mills said: “It is like a simmering pot ready to boil over. The staff’s greatest concern is that if there is a major violent incident, they will have to call the police who could take a while to get there.” In parliament, the prime minister backed Braverman’s handling of the issue, saying she has taken “significant steps” to address the problem of overcrowding at Manston. In a further development, the new human rights head at the UN has condemned Braverman’s claim that southern England faces an “invasion” of asylum seekers as “horrible” and “dehumanising”. On Monday, Braverman told MPs she was serious about “stopping the invasion” on England’s south coast, while referring to people who travel across the Channel in small boats and seek asylum. Volker Türk, who became UN high commissioner for human rights two weeks ago, said such terms were not appropriate. “We will really have to work very strongly (so) that it doesn’t poison … issues that are about human beings,” he said. A Home Office spokesperson said: “Manston remains resourced and equipped to process migrants securely and we will provide alternative accommodation as soon as possible.”