Prison bosses have denied that a young offenders' institute in County Durham hit by rioting has been badly run.
A wing was taken over by inmates at Deerbolt, near Barnard Castle, on Tuesday evening after warnings from the Prison Officers' Association of unrest.
The rioting was brought under control in the early hours of Wednesday and the Home Office has denied the youth jail is "under-resourced and undermanned".
On Sunday, four prison officers were injured at the same jail during a riot.
Insp Tony Bell, of Durham Police, said the latest disturbance was brought under control at 0030 GMT on Wednesday, about five hours after it began.
He said: "All the inmates are safe, there is no-one barricaded in and they are all under the control of the Prison Service.
"The disturbance was being dealt with by the Prison Service, the police were in attendance to see if any criminal offences were being committed.
"No arrests were made but it will be the subject of further investigation and arrests may be necessary."
A statement released on behalf of the Home Office said: "A full investigation will be taken by outside managers.
"Deerbolt was within its operational capacity, was not under-resourced and was not undermanned.
"A police investigation is also under way and it would be inappropriate to comment further while this is ongoing."
On Sunday one prison officer was left with a fractured skull, but there have been no reports of any injuries during the most recent disturbances.
The Prison Officers' Association said it had earlier warned management that the situation at the prison was volatile.
Steve Cox, national vice chairman of the association, said: "The fact that there have been two serious disturbances in the space of 48 hours has got to indicate that there is something drastically wrong in that institution.
"All prisons are overcrowded, all prisons have problems, but they don't all have riots night after night.
"There has got to be something seriously wrong to cause prisoners to act in that way."
Helen Attewell of the crime reduction campaign, SmartJustice, said less petty criminals should be sent to jail.
She said: "Overcrowding in the prison system is bound to cause tensions in institutions as offenders are frequently shunted hundreds of miles from prison to prison.
"The only long-term solution to the crisis is to stop sending so many non-violent petty criminals into jail and put more resources into punishments in the community, where offenders are made to pay back for the harm they've done."