A MOTORIST risked his life to rescue a man from an inferno at a crash site in which three men died.

A witness to the crash and its aftermath said: " I saw things I wished I had not seen."

Two victims were incinerated, another was thrown from the car and killed and a fourth was badly burnt when the car lost control and crashed into a gas main, which exploded in flames and ignited the fuel tank.

The 27-year-old male driver from Oak Flats and two of his passengers, a 24-year-old man from Farmborough Heights and a 19-year-old man from Brownsville, died at the scene in Wollongong on Friday night.

The car left the road, hit a power pole, smashed into a fence and landed on the gas main.

A passer-by pulled one of the passengers from the burning car and doused the flames with his car's fire extinguisher.

Police said the rescued man had burns to 50 per cent of his body.

He was taken by ambulance to Wollongong Hospital and then to the burns unit at Royal North Shore Hospital in Sydney.

The 21-year-old man from Dapto remains in a serious condition.

Police have not yet released the rescuer's name as he could be a witness in the crash investigation.

Acting Inspector Mark Walker said the passer-by had probably saved the man's life.

"His act was very heroic and we could recommend some sort of bravery award as he possibly risked his life to pull the bloke from the burning vehicle," acting Inspector Walker said.

Phil Peckman, 43, was working late in his industrial engineering business overlooking the Princes Highway when he heard — and felt — an explosion outside his window.

"I looked out the window and saw a huge fire and the car wreck was sitting on top of the gas main at the corner of our building," Mr Peckman said.

"I understand it was the gas main which set the car petrol tank off. The heat was so strong it forced me back from the window. It was very intense."

Mr Peckman was still shaking from the experience 18 hours later.

"My thoughts go out to [the victims'] families. I don't know how they can deal with this. I saw things I wished I had not seen."

He said he saw the man who helped rescue the passenger.

"The fire was really intense and flames shot into the air from the force of the gas," Mr Peckman said.

"I saw a guy with a fire extinguisher in his hands … This guy got out his fire extinguisher from his car and put out the flames on the guy who was burning."

The burnt man was soon taken away by ambulance, he said.