Crash investigators trying to piece together fatal crash that killed one, critically injured three others

Police are asking for public assistance after one person was killed and three were critically injured in a crash on the NSW South Coast.

A BMW SUV and a removalist truck collided at the bottom of Bulli Pass in Thirroul, a northern suburb of Wollongong, at about 1.50pm on Friday.

NSW Police confirmed the incident involved two vehicles on Saturday after early reports said the crash involved multiple cars.

Investigators on Saturday morning urged anyone with dashcam footage or information to come forward.

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Two men were thrown through the windshield of the truck during the collision, NSW Police confirmed on Saturday morning.

Earlier reports said three men were thrown from the vehicle.

A 43-year-old man who was killed was found below the overpass.

A 40-year-old man was trapped beneath the vehicle for more than an hour as crews worked to free him.

He was treated at the scene and taken to Liverpool Hospital.

The truck driver, 39, was airlifted to Westmead Hospital's trauma unit, where he underwent surgery.

A 40-year-old woman driver of a BMW SUV was freed from her vehicle by Fire and Rescue NSW and was flown to Sydney's St George Hospital.

All three patients were in critical conditions when taken from the scene.

Three fire crews attended the scene to cut passengers free from the vehicles.

Lawrence Hargrave Drive and Bulli Pass have both reopened in both directions after it was closed following the crash.

Debris from the crash had been spread across the neighbouring road, causing a build-up of traffic and road closures.

Police have established a crime scene, which will be forensically examined by specialist officers from the Crash Investigation Unit.