Diversions are in place on the N74 between Tipp Town and Cashel at Kilfeacle
The road remains closed following a single vehicle collision last night at around 8.30.
Three occupants of the car were taken to University Hospital Limerick. A male in his late teens is believed to be in a serious condition.
Gardaí in Tipp Town say the road is likely to be closed for a number of hours this morning while a forensic examination of the site is carried out.