A thief has stolen a new Holden Commodore during a company demonstration at Mallala Raceway, north of Adelaide.

Holden staff were conducting a training session with the new model Series II VF Holden Commodore SS about 11:30am when a woman drove on to the racetrack with another car with a passenger.

The male passenger was seen getting into the driver's seat of the demonstration vehicle.

Police said the keys were in the ignition of the white Commodore, which has a registration number of S-176-BIG, and the man drove out of the racetrack complex.

Witnesses detained the woman until police arrived.

The 28-year-old from Two Wells has been charged with driving while disqualified and has been bailed to appear in the Elizabeth Magistrates Court on December 3.

Police are looking for the man who is described as being Caucasian, between 20 and 30 years old, about 180 centimetres and having an average build and dark hair.

He was wearing a baseball cap, T-shirt and colourful board shorts.