Specially-trained prison security teams have been drafted in to deal with an "ongoing incident" at a jail.
So-called Tornado squads, equipped to deal with riots, have been sent to HMP Hewell near Redditch, Worcestershire, after trouble broke out on one of the prison's wings on Saturday.
The Prison Service said a "small number" of inmates at the category B jail were involved.
It is understood a handful of prisoners were refusing to follow prison officers' orders and had been attempting to cause damage to the wing.
Men shouting and swearing, as well as banging and dogs' barking, could be clearly heard coming from the scene late on Saturday.
From about 7.30pm, unmarked vans using blue lights and sirens started arriving at the site which is run by HM Prison Service.
A steady stream of vans and minibuses was seen arriving at the jail's front entrance, carrying and unloading Tornado squads carrying backpacks full of equipment.
The main site, which houses about 1,000 inmates - some of whom are category A remand prisoners - is surrounded by farmland.
Hewell jail, which opened in its current form in 2008, is made up of six housing blocks or wings - while there is a separate open prison called the Grange.
In an announced inspection report published in January, Hewell was described as "a prison with many challenges and areas of serious concern".
Peter Clarke, chief inspector of prisons, said the "main concerns at the closed site were regarding issues of safety and respect".
He said levels of violence were "far too high", communal areas "dirty" and many cells over-crowded, with some described as "filthy".
Almost two thirds (60%) had told the inspection team it was "easy" to get hold of drugs inside.
Inspectors also found levels of self-harm had increased, a quarter of prisoners "felt unsafe".
A Prison Service spokesman said: "We are currently managing an ongoing incident on a wing at HMP Hewell.
"A small number of prisoners are involved and there is no risk to the public."
The spokesman added: "We are absolutely clear that offenders who behave in this way will be punished and face spending extra time behind bars."
Meanwhile, several loud quickfire bangs, thought to be distraction bursts being used by the prison authorities, have also been heard at the scene as the disorder continues.
These have been greeted by loud shouts thought to be coming from inside the affected wing.