More than a dozen prison officers were taken to hospital after violence broke out at a facility for young offenders in southwest London.
Around 14 staff at Feltham Young Offender Institute were treated after the melee, which flared up at lunchtime on Friday.
The Ministry of Justice (MoJ) said there were no serious injuries, and praised “brave” prison staff for managing to bring the fracas under control “within 25 minutes”.
It is not known how many youngsters were involved, and the ministry gave no further details on what sparked the disturbance.
A HM Prison Service spokesperson said: “An incident at Feltham Young Offender Institute was quickly resolved by our brave and diligent prison officers. We will never tolerate violence against our staff and will punish those involved.”
Feltham is home to around 100 boys and young men aged between 15 and 21.
An inspection report published in June identified soaring levels of violence and self-harm, high use of staff force, poor care and long periods of lock-up in cells in Feltham A, which holds offenders aged between 15 and 18.
Peter Clarke, the chief inspector of prisons, found an “appalling” decline in standards at Feltham A in his report. Mr Clarke called for “fundamental” change at the institution and said: “Neither boys nor staff were safe.”
It prompted the government to halt new placements at the unit in the London Borough of Hounslow.
The MoJ said there had been a sustained reduction in levels of assaults on staff, self-harm and use of force between the start of May and the end of August, but there are no plans to return the establishment to full capacity.
