They were confronted by a mob – some armed with pieces of wood – inside Ashwell Prison in Rutland. Fire crews were also drafted in as plumes of smokes rose from inside the compound.
Order was restored by the afternoon and 80 rioters from the open prison were taken away.
A father of one inmate said: “He called me up to say it had all kicked off and that there was a riot and prisoners were setting fire to stuff.”
Brian Caton, general secretary of the Prison Officers Association, said the rioting was an inevitable consequence of cost-cutting.
He claimed only a “handful” of prison officers had been on duty to watch over 619 inmates when there should have been at least 24.
Last night it was unclear if any prisoners or officers had been hurt in the clashes.