A passenger of one of the cars, a man in his 20's, was taken to Cork University Hospital and is in a critical condition.
The driver of the other car, a female in her 50's, was also taken to CUH with serious but non-life-threatening injuries.
The road at McCurtain Street remains closed this morning for a technical examination with local diversions in place.
Gardaí are appealing for any witnesses to this collision to come forward.
Any road users who may have camera footage, including dash-cam, and were travelling in the McCurtain Street area between 8:30pm and 9pm are asked to make this footage available to Gardaí
Anyone with any information is asked to contact Fermoy Garda station on 025 82100, the Garda Confidential Line on 1800 666 111 or any Garda station.
