A man who was pulled from a burning vehicle on the Southern Expressway, in Adelaide's south, remains in a serious condition at Flinders Medical Centre.

Just after 4:30am an Audi sedan travelling south on the expressway crashed into the rear of a broken down van parked on the left side of the road, about 600 metres north from the Majors Road overpass.

The car caught fire on impact, with the 29-year-old driver from the southern suburbs pulled from the burning wreckage by a passing motorist.

He was the only occupant of the car.

The wreckage on the Southern Expressway has been cleared and all lanes are now open.

Police said the injured driver will be interviewed at a later date and called for witnesses to contact Crime Stoppers on 1800 333 000.