The Ministry of Justice is dealing with a disturbance at high-security Long Lartin prison after dozens of inmates attacked staff.
According to the BBC, up to 80 prisoners are involved in the incident and used pool balls as weapons.
Tornado teams of riot officers have been sent into the Category A prison in Worcestershire, which has a capacity of 622.
A Prison Service spokesman said: "We are currently managing an ongoing incident at HMP Long Lartin.
"We are absolutely clear that offenders who behave in this way will be punished and face spending extra time behind bars."