The incident involved two vehicles, which collided head on.
Three people have been taken to Cork University Hospital for treatment, where the driver of one of the cars, a 34-year-old man, is said to be in critical condition.
Two other men, the driver and a passenger in the second car, aged 56 and 17, received non-life threatening injuries.
The collision occurred on the R610 at Raffeen on Saturday night at about 9.15pm.
The road is currently closed as Forensic Collision Investigators are at scene, with local diversions in place.
Gardaí are appealing for anyone who was travelling on the R610 at Raffeen between 9pm and 9.15pm last night, or anyone who was in the area and may have witnessed the collision, particularly any road users with dash cam footage, to contact Togher Garda Station on 021 4947120, the Garda Confidential Line 1800 666 111 or any Garda Station.
