Twenty people have been on hunger strike for two days at an immigration centre in Bedfordshire in protest at the standard of medical care.
Detainee Melchior Singo, 39, of Malawi, said people in the family unit at Yarl's Wood stopped eating on Monday.
Meanwhile violence flared when a group of detainees were separated from other inmates.
It is not known if this was connected to the hunger strike, but two officers were reportedly injured.
Staff trained in "conflict resolution" separated a small number of detainees for "disrupting the normal operation of the site", a UK Border Agency official said.
"This separation was conducted with the utmost sensitivity and there have been no injuries to detainees," a spokeswoman said.
The hunger strike has been called amid claims that health care is "sub-standard" at the site.
The Home Office said 24-hour health care was available at the site and said it had been praised by independent inspectors.
Mr Singo said his nine-year-old daughter Olger was referred to an orthodontist before they were held at the centre, but has since been denied further treatment.
He said: "Medical attention is not given as a priority.
"We've got medical healthcare but we don't get the right care that we need.
"If you fall ill after lunch you can't see the nurse, even if it's urgent, until the following day."
The detainees are also protesting at children being held at the centre.
Following a visit to Yarl's Wood in April, Children's Commissioner Sir Al Aynsley-Green called for an end to the detention of children before deportation.
He said nearly 2,000 children were locked up in the UK each year solely for administrative reasons, and that the length of time they were being held was on the increase.
Yarl's Wood has 121 family beds, along with 284 single female beds, and a healthcare centre on site with a small in-patient ward, according to the UKBA.
A spokeswoman said: "A small number of detainees at Yarl's Wood have refused meals since lunchtime Monday.
"Some are accessing snacks through the night cafe and children are obtaining additional snacks in classrooms in the day.
"The situation is under control and we are discussing with detainees their concerns.
"Our centres have been praised by independent monitors and our medical care is as good as on the NHS.
"There is 24-hour nursing care, doctors on call night and day and access to social workers and dentists."