A car and truck collided on the Sturt Highway at Barmera, near Nookamka Terrace, just before 7.15am on Tuesday 21 July.
The truck rolled and is blocking the highway in both directions. A light pole was also knocked down. SA Power Networks will attend.
Motorists are advised to avoid the area if possible.
Traffic, including heavy vehicles, is being diverted around the scene via Morgan Road and the Goyder Highway and via the Monash turnoff.
Heavy vehicles entering SA through Yamba are advised to take Stanitzki Road to avoid the crash scene.
Anyone who witnessed the collision or has any dashcam or CCTV footage that may assist the investigation is asked to contact Crime Stoppers on 1800 333 000 or online at www.crimestopperssa.com.au