Security firm G4S is tackling an incident at Oakwood Prison.
It is an "ongoing incident" which has now been "contained", a spokesman said.
No further information was available about what had triggered the problem at HMP Oakwood, in Featherstone near Wolverhampton, which was the scene of a number of rooftop protests last year.
The G4S spokesman said: "We can confirm that there is an ongoing incident taking place on a wing at Oakwood prison.
"The situation is contained and we are applying standard procedures to manage the incident."
A spokesman for Staffordshire Police said the force was aware of the incident at the privately-run jail and was offering support and assistance to G4S.
More to follow...