Two children had their arms broken from staff use of force and there were high levels of violence and a number of routine strip searches at a young offenders prison, an unannounced inspection has found.
Just one of the 3,773 strip searches conducted during the 12 months before the inspection at HM Young Offenders Institution (HMYOI) Ashfield, near Bristol, resulted in a find.
There were high levels of violence too, with 43 serious fights in the year to January, Chief Inspector of Prisons Nick Hardwick said.
Prison reform campaigners said the inspection report was a "damning postscript to a long story of violence and harm" at the Serco-run jail.
HMYOI Ashfield, which held 123 young people, most aged 16 or 17, at the time of the inspection, is to be re-roled as an adult prison from July 1 following an announcement made by the Justice Secretary Chris Grayling earlier this year.
Mr Hardwick said plans for the closure of the site were not effectively co-ordinated and this may have contributed towards "tension" in the prison.
There had been 351 fights and 377 assaults in 2012, according to data supplied by the prison.
Out of 43 serious fights in the 12 months to January, 37 resulted in serious injury and six in minor injury. Five staff were also assaulted in the same period.
Use of force was high with 453 recorded cases in the six months prior to the February 2013 inspection, most of which related to fights and assaults.
Around 25% of recorded incidents involved full control and restraint, the inspector said, compared with 33% at the previous inspection.
During 2012, two young people had sustained broken bones following incidents where force had been used; these incidents were referred to the local authority and the police.
No external investigations were carried out but internal investigations were undertaken in both instances, the inspector said.
Frances Crook, chief executive of the Howard League for Penal Reform, said: "Far from being a place of security, this was a hotbed of violence and abuse where bones were broken, levels of self-harm soared and children were routinely subjected to invasive strip-searches.
"And yet, when asked by the inspection team if they felt unsafe, the children said no. So embedded was this culture of control by physical force that dangerous practices had become normal to them."
She added: "How many more boys and girls need to have their bones broken before the Government realises that prison is no place for a child?"
Ashfield, which with a capacity of 360 offenders was just one-third full at the time of the inspection, has seen inmate numbers drop from an average of 237 in 2012.
The prison holds young people from more than 120 sentencing courts covering the South West, Wales, the Midlands and the London area.
Michael Spurr, chief executive of the National Offender Management Service, said: "We will always seek to make the most efficient use of the prison estate and the fall in the number of young people in custody has created the opportunity for Ashfield to specialise in the treatment of sex offender prisoners.
"Public protection is our priority and I am committed to ensuring that we have a robust risk management system in place to allow for a smooth transition."
Juliet Lyon, director of the Prison Reform Trust, said: "Breaking bones and routine strip-searching are no way to treat vulnerable young people behind bars.
"This disturbing report shines a clear light on violence and self-harm in the closed world of a deteriorating young offender institution.
"Decisive action is needed to safeguard young people, end uncertainty for young prisoners and staff, and close this institution safely."
HMYOI Ashfield is now empty and will become a Category C adult male prison holding sex offenders.
Commenting on the incidents involving use of force that resulted in broken bones, a Prison Service spokesman said: "An external investigator found that the young people had sustained recent previous injuries to the same area, before the use of force by staff.
"The conclusions of the investigations did not identify any evidence to suggest staff had been heavy-handed."
Turning to routine strip searches, he added: "The safety and welfare of young people in custody is an absolute priority.
"Youth custody has undergone significant change and improvement in recent years - we have introduced a new search policy to ensure young people are not searched unnecessarily and restraint is only ever used as a last resort.
"We continue to closely monitor these issues."
Ray Duckworth, Serco's prison director, said: "The care and treatment of young offenders is challenging and involves looking after some of the most vulnerable and difficult young people in society.
"Most of the young people at Ashfield are a long way from home and the Chief Inspector's report acknowledges this demanding environment.
"In particular, we recognise that the past few months have been a very unsettling period for everyone at Ashfield.
"Importantly, the young people at Ashfield did not feel unsafe and we are pleased that the report acknowledges the professionalism of our staff and the efforts that they have made to provide a good environment, access to education and training and systems that address the particularly poor behaviour of some young people.
"All young offenders have now left Ashfield and we are now preparing for the new adult population."