A search is under way for two young offenders who escaped from the Oberstown children's detention centre last night.
Three youths detained at the centre attacked a member of staff with a crowbar before cutting a fence with an angle grinder and escaping.
Gardaí were called and one was returned to the centre while two others remain at large.
The director of Oberstown, Pat Bergin, was slightly injured during the attack.
A unit in the centre was damaged and has been closed.
It is the latest incident to occur at Oberstown, including industrial action by staff who have raised concerns about their health and safety, a rooftop protest during which a member of staff was injured, and a fire at one of the buildings at the campus.
Minister for Children Katherine Zappone confirmed this morning that an incident had taken place, which she described as disappointing.
She said a lot of progress had been made and that incidents at the children's detention centre were now less frequent, but she stressed that it was a detention centre and that there are risks.
The escape happened at around 9pm last night - the day the Government launched a plan entitled Oberstown 'Building the Future'.
The damaged unit has now been closed and the occupants moved to other units.
Meanwhile, the Irish Penal Reform Trust has called for a full investigation into what happened.
IPRT acting executive director Fíona Ní Cinnéide said the timing of the incident was disappointing given that there has been a relative period of calm at the facility.