A prison officer and an inmate have been taken to hospital following a disturbance in Mountjoy Prison this morning.
Two prisoners got involved in a row and when prison officers intervened, other prisoners refused to leave the area.
The incident happened on the A wing just after midday.
All prisoners on the wing were returned to their cells and all inmates at the prison have been locked in their cells.
The Prison Service says this is normal procedure at lunchtime.
It is the third incident at the overcrowded prison in the last 24 hours.
At around 7pm last night four inmates damaged toilets and washbasins on B wing.
A man is still in intensive care in Beaumont Hospital after he was found semi-conscious in his cell yesterday morning.
The 26-year-old old had been hit over the head with a sock containing batteries following a row with another inmate over a television remote control.
