Specialist officers have been sent into Long Lartin prison in Worcestershire after inmates attacked staff.
Prison officers were assaulted with pool balls by ten prisoners, forcing them to retreat from a wing of the jail .
One member of staff required hospital treatment.
A specialist unit, known as a Tornado team, has been sent in to try to restore order.
A Ministry of Justice spokeswoman said: “Specialist staff have been deployed to manage an ongoing incident at HMP Long Lartin.
“We are absolutely clear that prisoners who behave in this way will be punished and face extra time behind bars.”
Prison Officers’ Association general secretary Steve Gillan tweeted: “At (the) moment we do not know all the facts but we fully support all our members at Long Lartin who are clearly facing a difficult evening with a disturbance.”
HMP Long Lartin houses some of the country most dangerous offenders.
It has capacity for 622 prisoners , but currently holds around 500, a quarter of whom are classed as category A, or high security.
According to a 2018 report into the prison following a serious disturbance involving 81 prisoners, around 75% of the inmates were serving life sentences.
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