The Prison Service said all its prisons run a "safe and secure regime" after disturbances broke out at two jails yesterday.
A spokeswoman said:
The Prison Service says there has also been a disturbance at Rye Hill Prison, near Rugby in Warwickshire, but it was unrelated to the Maidstone Prison incident.
"There was a passive demonstration at HMP Rye Hill where around 60 offenders refused to return to their cells," she said.
"This was peacefully resolved within a few hours."
Criminologist Professor David Wilson said prison guards likely enacted Operation Tornado to bring the latest riot under control.
It is a proven method using specialist officers that has been used many times before, he said.
A Prison Service spokesperson has said the incident at Maidstone Prison has now been resolved.
He said: "An incident involving around 40 prisoners at HMP Maidstone has been successfully resolved with no injuries to staff or prisoners.
"An investigation is underway and the perpetrators will be dealt with appropriately by the prison."
Cuts of some £90 million to prison services in recent years are behind the riots at Maidstone Prison in Kent, the Prison Officers union has told ITV News.
"The reduction in staff numbers means there are fewer prison officers available to carry out a normal prison regime", Prison Officers Association vice chair Ralph Valerio said.
"This means that prisoners spend more time locked up in a contained space.
"That can get to you. Many of the inmates also have anger management issues," he said.
The current staff to inmate ratio at HMP Maidstone is 1:30, which meant the staff had to retreat quickly when the incident, involving up to 180 prisoners, began earlier today, Mr Valerio added.
Officers at Maidstone Prison "feared for their lives" and were forced to retreat amid a prison riot involving up to 180 prisoners, Prison Officers Association vice chair Ralph Valerio has told ITV News.
The incident is still ongoing but has been contained within the prison's Thanet Wing, Mr Valerio said.
An "on-going incident" is taking place at Maidstone Prison, said to involve "a number of prisoners". It is said to have been confined to one wing.
- HMP Maidstone has an inmate population of about 600
- It is a Category ‘C' training prison that predominantly houses sex offenders from the Kent and Sussex areas.
- Category C prisons are closed but have less internal security.
- The prison also takes in a small number of foreign prisoners with more than 18 months to serve