Ambulance and fire crews were called to Swinfen Hall prison and young offenders' institution at 19:37 BST.
The incident involves D wing at the prison, near Lichfield, with Staffordshire Police guarding the perimeter.
The jail holds up to 624 male adults aged between 18 and 25, serving between four years and life.
A Prison Service spokesperson said: "Staff are working to resolve an ongoing incident at YOI Swinfen Hall.
"Specially-trained staff and emergency services are attending the scene and the police have been informed."
Emergency services are currently on standby after a Staffordshire prison was placed on lockdown.