Four die in horror crash in SA

Four people from the same family, including two children, have died after a truck collided with their car in South Australia's mid-north.

The car attached to a caravan and the truck, which was towing a trailer, smashed into each other on the Augusta Highway, 2km south of Crystal Brook, just before 12.30pm 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 - all from the same family, died at the scene.

The driver of the truck and two of his passengers were been taken to hospital with non-life threatening injuries.

A fourth passenger is in a critical condition and was airlifted to the Royal Adelaide Hospital.

Major Crash Investigators are at the scene and the Augusta Highway will be closed for some time between Venning Road and Clements Road, with diversions in place.

The deaths take the States road toll to 27 as compared to 24 for the same time last year.