Inmates “threw paint and smashed fire alarms” during a disturbance at a young offenders institution.
The Prison Service said four prison officers suffered minor injuries in the trouble at HMYOI Aylesbury in Buckinghamshire.
Inmates “trashed” E Wing in protest over a lack of showers and time out of their cells, the BBC was told.
The Prison Service said: “Offenders who behave in this way will be punished and may face extra time behind bars.”
Ellie Saddington, whose partner is an inmate, told the BBC some of the men had leapt onto the wing’s safety netting and refused to come down.
The 19-year-old from Liverpool said her partner was not involved and went back to his cell but another prisoner had sent pictures and made calls about the riot from a banned mobile phone.
“There’s a new regime and they aren’t allowed any association during the week,” Miss Saddington said.
“So they can shower and exercise but then have been locked up all week. They had one shower on Monday and nothing since.
“On Saturday they weren’t allowed the weekend association where they can play pool, etc. This morning, they were allowed another shower but, when they were told they were going to be locked up again, with no explanation, lots of them refused to go back.”
The inmates then “trashed the wing”, Miss Saddington said, adding “they’ve thrown paint, smashed fire alarms and broken cameras”.
E Wing houses more than 70 young men aged up to 21 in the jail on Bierton Road.
A Prison Service spokesperson said: “Prison staff at HMYOI Aylesbury have successfully resolved a brief period of indiscipline today involving a small number of offenders on one wing.”
They said the trouble was “confined to one area of the prison” and the rest of the site remained secure.
Four prison officers were taken to hospital with minor injuries and have since returned to duty.
Last July, seven prison officers and one inmate were injured in a “brawl” at Aylesbury.
In November, the Independent Monitoring Board (IMB) blamed serious understaffing for an increase in violence at the site.