A grieving family has demanded answers after a man was killed when an out-of-control Audi crashed into the Uber he was travelling in.

Seamus Duignan, 28, was heading home in the rideshare after celebrating his birthday at a concert when a white Audi collided with the vehicle in Sans Souci in Sydney‘s south early Saturday.

Mr Duignan, the Uber driver, 20, and the man behind the wheel of the Audi, 42-year-old Tamati Gilbert, all died at the scene.

Police were called to a home in Gymea Bay at about 12.25am to conduct a welfare check, after Gilbert’s partner raised ‘grave concerns’ for his mental health.

Gilbert was found sitting in the Audi in the driveway but sped off before police could speak to him.

Ten minutes later, police received reports an Audi had flipped over a concrete barrier and landed on a blue Toyota Camry on Rocky Point Road, 13km away in Sans Souci.

CCTV showed the Audi travelling at ‘considerable speeds’ moments before the crash.

Separate footage captured the fiery moment of impact.

Seamus Duignan was heading home from his birthday celebrations when tragedy struck
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Seamus Duignan was heading home from his birthday celebrations when tragedy struck

Seamus was one of three men killed when an Audi crashed into the Uber he was travelling in
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Seamus was one of three men killed when an Audi crashed into the Uber he was travelling in

Kim Duignan has demanded a comprehensive investigation into the crash that claimed her son Seamus’s life.

‘There needs to be a complete inquest into what caused this crash,’ she told the Daily Telegraph.

‘I don’t want any other parent to have to go through this.’

Mr Duignan’s brother Sean described him as ‘a good man, brother and uncle’ who was ‘never in trouble, just a good man who loved a laugh’.

Dozens of shocked bystanders tried to help after the impact caused one of the cars to catch alight.

‘Grabbed the fire extinguisher, gave it to somebody and just checked that people weren’t trapped inside,’ one distraught woman told Nine News.

‘My main concern was trying to get people out and the car not blowing up and that’s it.’

The crash scene was confronting for emergency responders.

‘It was a horrific scene. We really feel for the families of all three persons and their loved ones,’ Detective Acting Superintendent Graham Hibbs said.

CCTV showed the Audi travelling at 'considerable speeds' moments before the crash
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CCTV showed the Audi travelling at ‘considerable speeds’ moments before the crash

Seamus Duignan was described as good man who loved a laugh'
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Seamus Duignan was described as good man who loved a laugh’

The mangled Audi was still at the scene hours after it  flipped over a concrete barrier and landed on a rideshare on Rocky Point Road at Sans Souci
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The mangled Audi was still at the scene hours after it  flipped over a concrete barrier and landed on a rideshare on Rocky Point Road at Sans Souci

‘I don’t think there were many cars on the road at that time and [it was] extremely unlucky for the people involved.’

Detectives and forensic officers remained at the crash scene on Saturday as an investigation was launched.

Police will investigate whether the Audi driver was under the influence of drugs or alcohol.

A report will be prepared for the coroner.

Captain Cook Bridge and Rocky Point Road remained closed on Saturday, causing major traffic delays and diversions.

Locals have demanded speed cameras along the notorious stretch of road and at both ends of Captain Cook Bridge.

‘In the 20 years I have been living here, there have been at least 120 accidents at this corner,’ one told Nine News.

Another added: ‘Unfortunately, it takes for people to die for change to be made. It’s not good enough.’

Anyone with information is urged to contact Crime Stoppers.