Police are investigating whether the car was street-racing another vehicle at the time of the crash.

The impact of the crash was so intense that the engine of the Subaru Impreza was flung from the bonnet.

Residents have recalled the 'deafening' noise of the crash that left their homes and windows shaking.

Some raced outside to pull the injured occupants from the vehicle.

The nine-year-old girl 'screamed for her daddy' as emergency services tried to save her young cousins.

'She was screaming 'get me out,' one man told Nine News.

'We were trying to open the other doors but we couldn't open them.'

Residents are still haunted by the harrowing scenes.

'We went to the right side of the car and we were able to get the little girl out,' Hadi Sawan told the Saturday Telegraph.

'On the other side, we weren't able to do that, it was jammed from the impact. I don't even want to explain what I saw out of respect for the families.'

'It's heartbreaking… but I was also scared, if it weren't for the tree the car would have ended up in my house or my neighbor's house.'

Shaima Bakr added: 'It was very scary seeing that.'

'Seeing [it] on the news usually, it's upsetting, but seeing it in real life was traumatic. I didn't want to go close to it ... hearing the little girl crying and asking for her dad and her uncle.'

The little girl remains in hospital in a stable condition and is expected to be interviewed by police in the coming days.

CCTV from a neighboring property captured the moment the car flipped and slammed side-on into a tree after it crossed the median strip.

Residents are seen racing to the scene of the wreckage moments later.

Police are investigating whether speed and street racing were factors that contributed to the crash.

They are hunting a grey sedan they believe may have been involved in the incident.

'At this stage, we will be seeking the assistance of members of the public to identify a grey sedan that was traveling in lane one around the time of the collision,' Detective Inspector Jason Hogan from the NSW Crash Investigations Unit said.

'That will be a significant line of inquiry for our crash investigators, to establish the speed of the vehicle, and that appears to be...a contributing factor.'

'It is a particularly nasty crash where two innocent young children have lost their lives.'

'We'll be in constant contact with all members of the family to ensure their welfare and that they're kept abreast of the investigation as it unfolds.'

The tragedy has prompted residents to renew concerns about 'drag racing' along Grand Parade in Monterey.

The speed limit along that strip is 60km/h.

Residents say they've been campaigning for speed cameras for several years.

Two boys – aged 10 and nine sitting in the back seat were freed from the wreckage and rushed to Sydney Children's Hospital at Randwick where they died shortly afterwards.