The driver of a truck that collided with a car in Sydney's southwest killing three of its five occupants was not at fault, according to NSW Police.
A 74-year-old man driving the car and a female and a male passenger died at the scene of the smash in Campbelltown on Friday.
The car slammed into the side of the truck causing it to veer off the road and into fences, Inspector Michael Moroney said.
"At this stage, we're examining all facets as to the reasons why the accident occurred," Insp Moroney told reporters.
"But it would appear ... the truck was not at fault and for some unknown reason the vehicle careered into the path of the truck."
All five people in the car were from the Sydney area.
NSW Ambulance Inspector Stephen Fulton says 11 ambulance units, including two rescue choppers, arrived to a "distressing scene".
"It was a confronting incident, the vehicles were badly damaged, there was debris everywhere and there were a number of distressed bystanders," he said in a statement.
Two passengers from the car were taken to Liverpool Hospital in a stable condition.
A 76-year-old woman suffered suspected spinal and chest injuries and a 45-year-old man suffered pelvic and chest injuries.
The 59-year-old truck driver was taken to Campbelltown Hospital for mandatory drug and alcohol testing.
Insp Moroney said the man was co-operating with police and wasn't injured.
There were also a number of witnesses which are giving statements to police, he added.
