South Australian police are investigating a horror crash which claimed the lives of two young girls and their grandparents.
A car towing a caravan and travelling north on the Augusta Highway collided with a truck towing a car trailer near Crystal Brook on Sunday.
All four people in the car, a 70-year-old man, a 59-year-old woman and two girls aged 5 and 10, died at the scene.
The 52-year-old driver of the truck was airlifted to the Royal Adelaide Hospital and remains in a critical condition.
Three of his passengers, a man aged 50 and two women aged 42, were all taken to the Port Pirie Hospital with less serious injuries.
Major crash officers are investigating the cause of the crash but the highway has reopened to traffic.
Police have already spoken to a number of people at the scene and will be also speaking with those taken to hospital.
An elderly woman has meanwhile died in hospital after a separate crash in SA's Riverland region.
The 82-year-old collided with a power pole on the Sturt Highway on Tuesday and died from her injuries at the Royal Adelaide Hospital on Saturday.
Police believe a medical incident may have caused the crash.
The two incidents take the SA road toll to 29, compared to 24 for the same time last year.
