A Limerick man, who is described as being "known" to gardaí, is in a critical condition in hospital after the car he was driving crashed through a roundabout and into a large advertising sign,
The 33-year old, from the Moyross estate, was driving a black coloured BMW Coupe 320, which was destroyed in the collision.
Gardaí do not believe any other vehicle was involved in the crash, which occurred on the N18, on the outskirts of Limerick city, between the Radisson Hotel roundabout and the Coonagh roundabout.
The crashed BMW was discovered by a passing motorist around 2.40am and they notified the emergency services.
The driver, who was found inside the car, was cut from the wreckage by firefighters attached to the Limerick City Fire and Rescue Service.
He was rushed by ambulance to University Hospital Limerick and was later transferred to Cork University Hospital.
The injured man is understood to have sustained critical head injuries in the impact of the crash.
The Ennis to Limerick inbound lane remains closed to allow garda forensic collision inspector conduct a detailed examination of the scene.
Gardaí at Mayorstone are investigating.
Appealing for witnesses Superintendent Derek Smart, Henry Street, said: "Anyone who was at the Ennis Road around the time in question, who was coming from the Ennis direction, and if they saw any vehicle driving at speed or saw anything suspicious to contact us."