Sophie Russon, 20, Eve Smith, 21, and Darcy Ross, 21, from Newport, and Rafel Jeanne, 24, and Shane Loughlin, 32, from Cardiff, were all reported as missing over the weekend.
According to police, the three women had been on a night out in Newport on Friday, where they went to the Muffler bar in Maesglas.
They, and the two men, were last seen together in a Volkswagen Tiguan in the Llanedeyrn area of Cardiff in the early hours of Saturday, March 4.
Officers found the car while searching along the A48 in St Mellons, shortly after midnight on Monday.
It is believed the car was involved in a crash and came off the A48.
South Wales Police has now confirmed that Ms Smith, Ms Ross, and Mr Jeanne died in the crash.
Two others – the force said – were taken to the University Hospital of Wales in Cardiff where they remain in a “critical condition”.
Although they were not named by the force, it is believed these are Ms Russon and Mr Loughlin.
Family members and friends shared tributes online to Ms Smith, Ms Ross, and Mr Jeanne, while a book of condolence has also been set up.
A South Wales Police spokesperson said: “South Wales Police is continuing to investigate a fatal road traffic collision on the A48 in the St Mellons area of Cardiff.
“Emergency services discovered a Volkswagen Tiguan vehicle at 12.15am on Monday, March 6 after the police helicopter, police and fire officers were deployed to the scene.
“Formal identification has taken place this afternoon and three people who died in the collision have been confirmed as being Rafel Jeanne, aged 24, from Cardiff, Eve Smith, 21, from Newport, and Darcy Ross, 21, from Newport.
“Two further people were taken to the University Hospital of Wales in Cardiff where they remain in a critical condition.
“Investigations are ongoing to determine the circumstances of the incident, including when the collision took place.
“The five individuals were the subject of enquiries by Gwent Police following a missing person report made during the evening of Saturday, March 4. A subsequent missing person report in respect of one of the individuals was made to South Wales Police on Sunday, March 5.
“Referrals have been made by Gwent Police and South Wales Police to the Independent Office for Police Conduct.”
Assistant Chief Constable Jason Davies of South Wales Police said: “Our thoughts are with the families of all those affected by this tragic incident.
“To ensure independent oversight, South Wales Police has referred the matter to the Independent Office for Police Conduct, as is usual in these circumstances.”