It is understood the four involved were travelling to a Leaving Cert party when the accident occurred.
A man in his 20s, who was driving the car, and three women in their late teens were in the vehicle when it was involved in the accident outside Clonmel around 7.30pm on Friday evening. No other vehicle was involved.
All four occupants were tragically killed in the accident.
Local reports indicated that the four suffered critical injuries and died at the scene.
Two of those involved are understood to be siblings.
The Irish Independent understands the three teenagers in the car were all classmates who had just received their exam results.
A garda forensic investigation is now underway in Clonmel this morning after the crash last night.
Local priest Fr Michael Toomey spent last night with families affected by the tragedy and visited the scene this morning.
He said the community is in shock.
“Sometimes no words seem adequate when a tragedy like what occurred in Clonmel happens. No words can give comfort at this time.
Schools in the area have put critical incident plans into action and are liaising with each other about how to support students and the wider community.
“The families are devastated and in deep shock at the moment. We must keep them in our thoughts and our prayers, and indeed the community has been doing that,” Fr Toomey said.
He also paid tribute to gardaí and emergency crews who attended the scene last night and support the families of those killed in the crash.
“All the emergency services were fantastic last night. Obviously it is something they never want to see or deal with.
“As a community we are devastated and shell shocked. A number of events here this weekend or in nearby villages have all been cancelled now as a mark of respect.
“We are just looking out at the moment and my job now is to coordinate with the schools, their friends and immediate family to come have a safe space to gather and to grieve.
“It’s a sudden heartbreak. It’s something you can’t put into words.”
He urged any students and families in the area who are impacted by the tragedy and feel they need support to reach out to others, including the local schools.
The scene of the crash remains cordoned off this morning with roads closed in the area to facilitate an ongoing garda investigation.
The car remains at the scene.
Among the events cancelled is a local Pride parade due to take place today.
Organisers said their thoughts were “consumed by the profound loss that has befallen our town”.
Local Independent TD Mattie McGrath described the incident as “devastating” for the local community and “every parent’s worst nightmare”.
“Every Parents worst nightmare as gardaí have confirmed a number of fatalities,” Deputy McGrath said.
“Absolutely devastating news breaking in Clonmel. Our thoughts and prayers are with all those involved in this awful tragedy, their families, friends and classmates and the entire school community in Clonmel.
“Such a heartbreaking time and such devastating news for all students and their families. Devastating.”
Tánaiste Micheál Martin said the crash in Clonmel was “heartbreaking”.
“Deeply saddened by the tragic, heartbreaking loss of four young lives in Clonmel. Our thoughts and prayers are with their families, friends, classmates, the first responders, and the entire community today,” Mr Martin said.
Extensive damage was caused to the vehicle in the collision and, because of where it left the road, emergency services initially had difficulty in accessing it.
In a statement, gardaí confirmed: ”The bodies of the deceased have been removed from the scene to South Tipperary General Hospital and post-mortem examinations will be conducted in the coming days.”
The collision happened on the Mountain Road on the southern approach to the town.
Initial indications are that the vehicle involved may have spun out of control and then overturned along a very steep part of the road.
Garda Forensic Collision Investigators (FCI) have been requested to conduct an examination of the scene which will take place today.
An incident room has been established at Clonmel Garda Station and a Senior Investigating Officer has been appointed to lead the investigation.
Images of the immediate aftermath of the collision have been shared on social media.
“An Garda Síochána are appealing to the public not to share any of this material, if received, out of respect for the privacy of the deceased and their family and friends,” a spokesperson said.
Clonmel’s Mayor, Councillor Richie Molloy, said that the town was numbed by the tragedy.
“It is really shocking news. As a parent myself I can only imagine what the parents of these young people are going through,” he said.
“At this stage we do not know who was involved but I know that there are a number of families receiving the most awful and tragic of news tonight.
“Today was a happy day for the young people who received their Leaving Cert results.
“This has cast a cloud of sadness and grief over the entire community both young and old. Everyone is thinking and praying for the families at this time.”
The Mountain Road is notorious locally for having a very steep incline in parts.
It links the south Tipperary town with Waterford and the eastern section of the Knockmealdown Mountains.
A major emergency services response was dispatched to the collision with multiple ambulances, Tipperary Fire Brigade and Garda units at the scene.
The Coast Guard’s Waterford-based Rescue 117 helicopter was also on standby.
Gardaí closed the road involved to facilitate the work of the emergency services.
Motorists have been urged to avoid the area with local diversions being put in place.
A major emergency response was also triggered in South Tipperary General Hospital with standby medical support in both University Hospital Waterford (UHW) and Cork University Hospital (CUH).
Gardaí are appealing for any witnesses to this collision to contact the investigation team.
Any road users who may have camera footage (including dash-cam) and were travelling in the Mountain Road area between 7pm and 7.45pm are asked to make this footage available to gardaí.
Anyone with any information is asked to contact Clonmel Garda Station on 052 617 7640, the Garda Confidential Line on 1800 666 111, or any garda station.