A disturbance involving about 40 inmates from the same wing at Maidstone Prison has been resolved, the Ministry of Justice has confirmed.
National resources were deployed to deal with the incident at the Kent jail.
A prison services spokeswoman said the incident had been resolved without any injuries to staff or prisoners.
The incident was earlier reported to have involved up to 180 prisoners, but the spokeswoman said only about 40 prisoners were involved.
There was no evidence of damage reported either, she said.
"An investigation is under way and the perpetrators will be dealt with appropriately by the prison," she said.
Maidstone, with an inmate population of about 600, is a category C training prison that predominantly houses sex offenders from the Kent and Sussex areas.
The prison also takes in a number of foreign prisoners with more than 18 months to serve.
Prison Officers Association vice chairman Ralph Valerio said he had heard from staff on the scene mostly foreign prisoners were involved.
Mr Valerio said the riot was sparked by new regime changes and staff cuts that resulted in prisoners having to spend more times in their cells.
"Try to put yourself in the shoes of the offender - you find yourself spending more time locked up with less time to be able to call your family and less time to be able to have social interaction with the staff and with other offenders on that wing then it can have a detrimental effect," he told Sky News.
"As a trade union we have been warning against this for some time.
"The prison system is going through a tremendous amount of change at a tremendous rate of pace and it's a warning that the rate of change is unprecedented."
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.
"These are very well-tested systems and so it will be about trying to bring order back to HMP Maidstone."
"In these situations it's usually a question of being some particular incident that ignites the prisoners who want to take this kind of action and sometimes that action gets out of control."
Mr Valerio said the staff were well trained to deal with the situation.
"We have a contingency plan, the prison service is very, very good at dealing with these sorts of situations and the staff involved in that situation are highly professional," he said.
Fire and police crews were also called to attend.