Detective Sergeant Jeshua Kelly said detectives from the Major Crash Investigation Unit were investigating the cause of the single-vehicle crash on the Stuart Highway about 10km south of Larrimah.

"A passing truck driver noticed the vehicle off the road around 6:30pm on Monday, August 1 and reported it to police, but we don't know exactly when the crash happened," Det Sgt Kelly said.

"It's possible that other motorists passed the scene without realising it was a crash, so we're asking anyone who was travelling in the area on Monday to think back, check your dash-cams, and contact police if you remember anything about a grey Mitsubishi Pajero on the eastern side of the highway south of Larrimah."

Anyone with information is asked to contact Police on 131 444.