Inmates at a "crisis" prison caused a serious disturbance lasting more than eight hours.
The Prison Officers' Association (POA) said a fire was started during the incident at HMP Ranby in Nottinghamshire yesterday.
A spokesman for the Prison Service said minor damage was sustained and there were no injuries to staff or prisoners.
Chief Inspector of Prisons Nick Hardwick said HMP Ranby was ''in crisis'' after the publication of a report on Thursday which described the prison as unsafe with high levels of violence.
Glyn Travis, assistant secretary of the POA, described the disturbance as a "serious incident".
He said: "One hundred and twenty prisoners refused to return to their cells. They have taken control of a unit."
Mr Travis added that the inmates started a fire which was quickly put under control.
A Prison Service spokesman said: " A disturbance on one wing at HMP Ranby has ended. No staff or prisoners were injured and minimal damage was sustained.
"Prison staff were deployed to deal with the incident, which involved between 30 and 60 prisoners.
"The prison will now return to normal operation and visits will take place as usual today."
The disturbance began at around midday on Saturday and was not resolved until 8.10pm.
Prison staff are working with Nottinghamshire Police to identify the ringleaders.
Police, ambulance and fire crews attended the prison, which is on a country road a few miles outside Retford.
Officers carrying shields and other equipment were seen going inside, later joined by around 15 firefighters in their full kit.
Several p risoner-carrying vehicles went into the prison to collect a number of inmates, who could be heard shouting and banging as they were driven away.
A critical report on HMP Ranby was released following an 11-day inspection by HM Inspectorate of Prisons.
It found that two prisoners died through ''self-inflicted deaths'' last year, and a further two have died in a similar way since the unannounced inspection in March.
Conditions in part of the prison, which holds more than 1,000 men, were dirty, prisoners were found to have climbed netting in a bid to force a transfer to another facility and nearly half the population said they had felt unsafe having been victimised or intimidated, findings showed.
Evidence was found of an increasing number of incidences of self-harm at the category C training prison, and the availability of legal highs was also found to have increased.
Labour MP John Mann, whose Bassetlaw constituency includes the prison, said his repeated warnings that "dysfunctional" management and serious staff shortages would lead to disaster had been ignored by ministers and prison officials.
He said there were 80 fewer prison officers than previously - a 20% reduction - with many experienced individuals having been "forced out" over the past two years.
"It is a prison where, for quite a time, it's been clear prisoners have been running the prison," he said.
"There are not the numbers or the expertise among the staff to deal with it.
"The governors were warned, the Government was warned, by me and by many others, that this would lead to disaster.
"I have raised this directly with the prisons minister more than once."
He welcomed the appointment of a new governor but said he had "lost track" of how many changes there had been at the top and insisted the only solution was to recruit more staff.
Mr Travis said the disturbance was "no surprise" to the POA.
"It's all down to chronic staff shortfalls and a management that are hell-bent on delivering things they can't deliver safely," he said.
"Prisoners are saying 'We're not dealing with this'.
"They will react."