Two of the occupants of one of the vehicles involved - a man aged in his 20s and a man aged in his 30s - were pronounced dead at the scene.

Their remains have since been removed to Letterkenny Univerity Hospital where post-mortem examinations will take place in due course. 

A further two occupants of the same vehicle - a woman in her 20s and a man in his 20s - were taken to Letterkenny University for treatment of injuries believed to be non life-threatening.

Two occupants in the second vehicle involved - a man and a woman in their 40s - are also being treated for non-life-threatening injuries at Letterkenny University Hospital.

Garda forensics are due to undergo a technical examination of the scene and the road has been closed.

Fatal crashes in Loughlinstown and Muff

In Dublin, a woman died after being struck by a car late on Saturday night. 

Gardaí say the fatal collision occurred on the N11 Bray Road in Loughlinstown at approximately 11.50pm when a car hit a pedestrian.

The pedestrian, a woman in her 20’s, was pronounced deceased at the scene.

The coroner has been notified and the scene has been reserved pending an examination by Garda Forensic Collision Investigators. Local traffic diversions have also been put in place in the area.

A man in his 20s also sustained serious injuries in a crash in Muff on Co Donegal on Saturday night. 

The single-vehicle crash happened on the R238 at Ardmore at around 9.45pm.

The driver and only occupant of the car, a man in his 20s, sustained critical injuries in the crash and was subsequently brought by ambulance to Altnagelven Hospital in Derry. 

On Sunday morning, gardaí confirmed the man had passed away in hospital. 

The road remains closed and the scene will be examined by members of the garda technical bureau. 

Diversions are in place on the R238 from Muff Village via Iskaheen coming back out on the R238 at the Carmen Inn.

Gardaí have issued an appeal for witnesses to all four crashes, with anyone who may have any information urged to contact the Garda Confidential Line on 1800 666 111, or any Garda Station.

Investigations into the incidents are ongoing.