Conditions have deteriorated at an immigration removal centre to such an extent that it is a "place of national concern", the prisons watchdog says.
Nick Hardwick, chief prisons inspector, said Yarl's Wood, in Bedfordshire, was failing vulnerable women.
He said the concerns showed women, including pregnant ones, should be detained only as a last resort.
A Home Office spokesman said it was "committed to treating all detainees with dignity and respect".
Yarl's Wood holds more than 350 detainees, most of them single women, who are waiting for their immigration status to be resolved.
Mr Hardwick's report suggests that conditions have worsened since inspectors last visited two years ago. More than half of the detainees who were surveyed said they felt unsafe.
Mr Hardwick said that while a total of 443 women held at the centre were removed from the UK in the six months before the inspection, just over twice that number were released back to the community.
Of the 99 pregnant women who were held at Yarl's Wood last year, only nine were removed.
Fifteen detainees had been held for between six months and a year. Four were detained for more than a year, the longest being 17 months.
Yarl's Wood: A controversial history
- Opened in 2001 at a cost of £100m to hold some foreign nationals who are facing removal from UK
- Contains secure accommodation for 410 people
- Burnt down three months after it was opened during protests by detainees
- Run by Serco, with health services provided by G4S
- Repeated allegations of abuse, poor health care and inappropriate sexual contact, as well as protests, including hunger strikes
Mr Hardwick called for a "strict time limit" on how long anyone can be detained.
"Yarl's Wood is rightly a place of national concern. While there have been instances of unacceptable individual behaviour, most staff work hard to mitigate the worst effects of detention and women told us they appreciated this.
"These are issues that need to be addressed at a policy and strategic management level. We have raised many of the concerns in this report before.
"Decisive action is needed to ensure that women are only detained as a last resort. Other well-respected bodies have recently called for time limits on administrative detention, and the concerns we have identified provide strong support for these calls."
The Home Office has commissioned the former prisons ombudsman, Stephen Shaw, to independently review welfare in detention and he will report in the autumn.
A Home Office spokesman said: "A number of the findings in this report are extremely disappointing. Working with our partners, we want to make sure standards in the centre improve, especially regarding the provision and delivery of healthcare.
"We are committed to treating all detainees with dignity and respect. We aim to protect the health and wellbeing of those we are detaining at all times so we are pleased that this report finds that 80% of detainees surveyed said staff treated them with respect.
But Emma Ginn, of charity Medical Justice, said: "Immigration removal centres are dangerous places for many vulnerable detainees. They should be closed on health grounds while a comprehensive and independent investigation is carried out."
And Jerome Phelps, of campaign group Detention Action, said: "It is high time for the government to step away from the routine detention of migrants, and instead to work with them to resolve their immigration cases in the community wherever possible."