A man believed to be in his late 20s is on a life-support machine following a fight among a large group of people at an official Traveller halting site in west Dublin.
The incident was believed to be part of a feud involving a number of families.
The incident took place in the early hours of yesterday morning at Oldcastle Park, off Bawnogue Road, Clondalkin, Dublin.
A Garda van was patrolling the four-acre site throughout Saturday and in the early hours of yesterday, including the time of the row, as garda∅ said there had been disturbances throughout Saturday.
Garda∅ were yesterday removing a number of implements from the site, but these were not necessarily involved in the incident, Det Supt Tony Sourke told The Irish Times at the scene.
He said there had been "a dispute involving two families, and there was an altercation between the injured man and another man".
Members of other families were also involved, said Det Supt Sourke.
A man who had sustained serious head injuries was removed from the scene by ambulance and taken to Tallaght Hospital where his condition was described by staff yesterday evening as "dangerously ill".
Det Supt Sourke said there had been unrest in the area on Saturday. The Garda helicopter also monitored the site.
At the time the man received his injuries, Det Supt Sourke said, there was a Garda presence at the site, but he added that the garda∅ were monitoring and patrolling the entire site.
Once the garda∅ had heard an incident had developed, they responded immediately and assisted with the removal of the injured man, he said.
One resident of Oldcastle Park, who did not want to be named, said the incident was "a silly misunderstanding that got out of hand".
The disputes which occurred throughout Saturday "were not too serious until this terrible thing happened", he said.
There are between 300 and 400 residents on the site, living in 40 or 50 caravans.
The site this year won the award for best residential caravan park in the South Dublin Council tidy district awards.