A driver involved in a “horrific” triple-fatal crash in Sydney’s south overnight was visited by police just moments earlier following a concern for welfare incident.

Police were first called to a concern for welfare incident, on mental health grounds, at Gymea Bay at about 12.25am today.

Upon arrival, Acting Superintendent Graham Hibbs said that they found a 42-year-old man in the driver’s seat of a white Audi sedan.

Two drivers and a passengers died at the scene.© 9News

When police arrived one of the cars was found on its roof.© 9News

“Before police had the opportunity to speak with that male person, he left the scene,” he said.

About 10 minutes later, emergency crews were called to a “horrific scene” on Captain Cook Bridge at Sans Souci after receiving reports of a two-vehicle crash, with one car on its roof.

When police arrived at Rocky Point Road, they found that the white Audi sedan had collided head-on with a blue Camry sedan after travelling at what police believe was “considerable speed”.

“Tragically, the occupant of the white Audi was found to be deceased by police, as were the two occupants of the blue Camry,” Hibbs said.

The two men inside the Toyota Camry are yet to be identified.

Hibbs said that there were up to 40 people, including witnesses and onlookers, trying to help the men when police arrived.

Acting Superintendent Graham Hibbs.© 9News

“From what I understand, some of the bystanders rushed over to offer assistance, what minimal assistance they could offer in the circumstances, unfortunately.”

Hibbs said the onlookers helped put out a fire that had erupted within the engine bay of one of the cars.

Police are now looking at the potential that drugs or alcohol played a role in the triple-fatal crash.

The road was closed following the crash, but reopened about 11am this morning.