The surviving occupant of the car, a 21-year-old male, was rushed to Wollongong Hospital and was understood to have third degree burns to 50 per cent of his body.

Witnesses told the Mercury they saw a dark coloured sedan travelling south along the Princes Hwy about 7.15pm when it lost control near Orangegrove Ave.

``It was just flying down the road and then I saw the back lights just flipping around and then a few seconds later it burst into flames,'' a nearby resident said.

``You have no idea how fast it was going and then you could hear this massive bang.''

Chief Inspector Danny Sharkey of Lake Illawarra police said the vehicle, which had not been identified last night, had left the road, hit a power pole, landed on a gas pipe and burst into flames.

``At this time it appears that three occupants of that vehicle are deceased and one is receiving treatment at Wollongong Hospital,'' Chief Insp Sharkey said. ``I am unable to release any details about the occupants at this point in time.

``Suffice to say that the vehicle was severely burnt as well as the fact, that as a result of that accident a gas pipeline has been damaged and there is currently gas leaking in that area.

``It is very, very early in the investigation and I would not like to speculate on how it came about,'' Chief Insp Sharkey said.

The Princes Hwy at Unanderra was closed until at least 5am this morning as crash unit investigators worked to determine the cause of the accident.

Chief Insp Sharkey said many homes in Unanderra and Farmborough Heights had lost electricity as a result of the crash, but Integral Energy was on the scene and working to fix the problem.

More details on the story as they become available will be published on the Mercury website.