A protest by prisoners is underway at in Cloverhill Prison in West Dublin.
The Irish Prison Service says 2 men have climbed onto the roof of the jail.
The incident began when about 10 prisoners staged a protest, causing some damage to an area in the exercise yard.
The area was placed on lockdown and some 60 prisoners remain in the yard.
A spokesperson for the Irish Prison Service said prison staff are now working to bring the situation under control.