Specialist riot-trained officers have been deployed to a prison for the second day running after inmates reportedly seized control of a wing.
As the new disturbance erupted at HMP The Mount in Hertfordshire, staff also had to resolve an incident at HMP Erlestoke in Wiltshire.
Prisoners armed with weapons were said to have taken over The Mount's Nash wing, which houses up to 250 inmates.
Personnel from the Tornado team were called in again less than 24 hours after spearheading efforts to restore order at the Category C adult male training prison.
A Ministry of Justice spokesman said: "Specially trained prison staff have been deployed to HMP The Mount to resolve an incident involving a number of prisoners.
"The situation at the prison remains contained and there is no risk to the public."
On Monday multiple prisoners were involved in a lengthy disturbance across two wings at the jail, which holds a total of just over 1,000 men.
The first episode was resolved shortly after 10pm. No staff or inmates were injured, but dozens of cells are reported to have been damaged.
Monday's trouble broke out on the same day that a watchdog warned that the prison has struggled with "severe" staff shortages.
An assessment from the jail's Independent Monitoring Board said that last summer "all the ingredients were in place for The Mount to suffer disorder such as has been experienced in other prisons – staff shortages, readily available drugs, mounting violence".
Despite the shortages, the IMB said the establishment ended the year as a safe prison where inmates have a good chance of rehabilitation.
But it warned that drugs are "readily available" at the establishment in Bovingdon, Hemel Hempstead, with the substance known as Spice described as a "big concern".
Meanwhile, the Prison Service confirmed that staff had successfully resolved an incident involving a small number of prisoners at HMP Erlestoke on Tuesday.
The trouble flared less than a week after figures laid bare the scale of the safety crisis that has engulfed jails across England and Wales in the last year.
There were 26,643 assaults in the 12 months to March, including a record 7,159 attacks on staff - equivalent to nearly 20 every day.
Campaigners and watchdogs have issued a catalogue of warnings about violence, drug use and overcrowding across the jail estate.
Last month Peter Clarke, the Chief Inspector of Prisons, said staffing levels in many establishments are too low to maintain order and described the conditions some inmates are held in as "squalid, dirty and disgraceful".
The Prison Officers Association called for an independent review.
Mark Fairhurst, Acting National Chairman of the POA, said: "The Prison Service is in disarray; this type of unrest underlines the problems in our prisons and has significant ramifications for the taxpayer and local community."