Women at Yarl's Wood Immigration Removal Centre have been on hunger strike since Friday in protest at the length of their detention and poor living conditions.
Just before 5pm yesterday, one of the protesters, Aisha, said guards had locked most of the women in a corridor.
Speaking on a mobile phone from inside the Bedfordshire centre, she said: "We are in the hallway locked in. We have been here for five hours. There's no ventilation, no food, no nothing.
"We just wanted to protest about they way we are being treated by doing the hunger strike. We are having a lot of problems in this centre and we wanted to protest and explain our grievances but they are not going to listen."
Another detainee, Victoria, said: "I have heard that some people have been arrested but I am not with most of the others. They have been locked in a corridor and I am not allowed to go there."
She added: "We need the British Government to stop long-term detention. I have been in this centre for 15 months."
Protesters estimate their number at 70-100, although the UK Border Agency (UKBA) says it is fewer.
"Around 40 women at Yarl's Wood are protesting against their detention and have been separated from other detainees, while staff try to resolve concerns raised by these individuals," said David Wood, strategic director of criminality and detention group, for UKBA.
"The wellbeing of detainees is of paramount concern to UKBA, which is why healthcare staff are at the scene to monitor developments. The detainees will be integrated back into the centre at the earliest opportunity."
Earlier, the women issued a list of demands through the National Coalition of Anti-Deportation Campaigns, a group which calls for the release of all immigration detainees.
The women's demands include fairer immigration hearings, better access to bail for detainees and better medical care in detention. They also said Britain should "put the law into practice" by ending indefinite detention and called on the Government to "stop the forceful removal and the degrading system of deportation of detainees."
The women demand the end of detention for torture and rape victims and the release of all children, a call supported by many doctors and children's charities.
Yarl's Wood, run by private firm Serco, holds up to 405 detainees and is the main location used by the UK Border Agency for holding women and families.