Winchester prison: Inmates breach 'weak walls' in mass cell breakout
Nineteen prisoners escaped from their cells by using furniture to break "weak points" in the walls, the Ministry of Justice (MoJ) has said.
Police and specialist prison officers were called to a disturbance at HMP Winchester in Hampshire on Tuesday.
They used pepper spray to restrain two of the inmates, an MoJ spokesman said.
No-one is believed to have been injured, although four inmates were taken to hospital "as a precaution".
The prisoners broke out of their cells by "manipulating weaknesses" in the mortar around the doors, the spokesman said.
The prison officers' National Tactical Response Group, which handles potentially serious incidents, was called in to restore order.
Last month the MoJ gave HMP Winchester, which was built in 1846, its lowest performance rating, highlighting "serious concerns" about violence and inmate safety .
In a statement, the Prison Service said it would push for the "strongest possible punishment" for those involved in Tuesday night's disturbance.
It added: "We are urgently taking action to improve and modernise our Victorian jails - spending up to £2.5bn to create 10,000 new prison places and investing £100m to boost security and safety."
The MoJ said a full assessment of the whole prison would be carried out to prevent repeat incidents.
The prison's latest Independent Monitoring Board report in September 2018 said: "Cells regularly need repair because of wear and tear or vandalism."
HMP Winchester has two parts - a traditional category B Victorian prison holding up to 561 prisoners and the smaller West Hill site with 129 category C inmates.