A man's decomposed body was found over a week after the vehicle he was travelling in rolled off a road towards Verena, near Witbank, Mpumalanga police said on Saturday.
The Chevrolet Spark was found lying on its roof down an embankment, said Sergeant David Ratau.
"The car was so hidden that a person driving on the road or even walking past there would have a hard time seeing it. But one person saw it and alerted the police on Friday," said Ratau.
The identity of the badly decomposed man was yet to be verified.
Ratau told News24 that through the license plate of the vehicle, they had managed to trace the owner of the car who is from Kriel.
It was understood that he had lent the vehicle to a friend while they were in Siyabuswa on February 28.
His friend never returned the car.
The man claimed to have received information that his friend had been kidnapped by a group of men who had also taken off in his vehicle. He went to the Siyabuswa police station where he opened a case of kidnapping.
Ratau said it was unclear whether the corpse found in the vehicle was that of the friend or one of his alleged kidnappers.
The family of the man who borrowed car were expected to come and view the corpse for possible identification.
"If they can't identify him, then we will do DNA tests," said Ratau.