An incident lasting more than five hours at the country's largest prison has been resolved, security firm G4S has said.
The trouble broke out on a wing at HMP Oakwood in Featherstone, near Wolverhampton, yesterday evening, but the operator of the privately-run prison would not give any further details.
The incident was contained by staff before being resolved shortly after 2am.
HMP Oakwood, which houses more than 1,600 category C prisoners, was the scene of a number of rooftop protests last year and was slammed by inspectors during a surprise visit.
A G4S spokesman said: "This incident was resolved successfully at 2.10am.
"Police and internal investigations will now take place.
"It would be inappropriate to comment further until these have been completed."
The spokesman said earlier the company was applying standard procedures to manage the incident.
A spokesman for Staffordshire Police said the force was offering support and assistance to G4S.
The prison - the largest in England and Wales - opened in April 2012 as a training prison next to the existing HMP Featherstone and HMP Brinsford near Wolverhampton.
In a report published in October, HM Inspectorate of Prisons (HMIP) reported inexperienced staff and high levels of violence and self-harm at the jail - dubbed "Jokewood" by prisoners.
Chief Inspector of Prisons Nick Hardwick warned here were "real risks if matters were allowed to drift" at the prison.
At the time G4S said improvements were being made but admitted launching the prison was a "complex and challenging operation".
G4S - well-known for its botched handling of its Olympics security contract - has been under review by the government following revelations it overcharged for criminal-tagging contracts.
The government has since announced that electronic monitoring will handed to another firm on an interim basis at the end of the financial year.
G4S said later that the company had not previously claimed the disturbance lasted for five hours and described the reports as "speculation".