A SURVIVOR of an horrific highway crash which killed two people and injured five near Woodburn has undergone surgery as police struggle to determine how the incident occurred.
The 34-year-old woman and another survivor, a 69-year-old man who was still in a hospital high dependency unit yesterday, both underwent mandatory blood and urine testing after Saturday's crash.
A 41-year-old man and 72-year-old woman died at the scene and police were working to establish their identities.
If you saw the crash or the events leading to it, phone Ballina Police on 02 6681 8699 or Crime Stoppers on 1800 333 000
Three children also suffered minor injuries in the crash, which occurred about 11am on the Pacific Hwy about two kilometres south of Woodburn.
NSW Police said the incident involved a southbound B-double truck, a northbound Holden Colorado towing a trailer, which the 41-year-old was driving, and southbound SsangYong 4WD towing a caravan, which the 72-year-old was a passenger in.
The 50-year-old truck driver was not injured, but was taken to Lismore Base Hospital where he underwent mandatory blood and urine testing.
Debris, including drink bottles, a child's seat and pieces of the caravan, were strewn across the road at the crash scene.
The accident was attended by Woodburn RFS volunteers, Woodburn SES volunteers, Evans Head Fire Brigade, Ambulance Service of NSW, Westpac Life Saver Rescue Helicopter and NSW Police.
Traffic was diverted via the Bruxner Hwy and Summerland Way until the Pacific Hwy was cleared in the early evening.
Richmond LAC Duty Officer Inspector Steve Underhill said no charges had been laid, but a comprehensive investigation was underway.
It is understood officers are struggling to comprehend the series of events leading to one of the worst crashes many local emergency workers have attended.
Northern Rivers Rural Fire Service Superintendent Boyd Townsend said the crash was "... as close to as bad as it gets".
Investigators are appealing for anyone who may have witnessed the crash or the events leading up to it, to come forward.
The crash brings the road toll in the Richmond Local Area Command to 13 since the year began.