A woman in her twenties has died following a crash involving one car on Saturday at about 12.40am.
The crash happened on the N3 at Drumalure, Belturbet in Co Cavan.
Another passenger, a man also in his twenties, was taken to Cavan General Hospital in a critical condition.
The driver, a man, and two other women passengers, also in their twenties, were taken to hospital with non-life threatening injuries.
The scene is closed for a technical examination.
Gardaí are appealing for anyone with information to contact them at Cavan Garda station on 049 436 8800 or the Garda confidential line on 1800 666 111.
The matter has been referred to Gsoc as the car was subject to interaction with gardaí prior to the crash.