Police remain baffled how a truck driver they thought had been killed in a fiery crash showed up alive more than 30 hours later, 16 kilometres away from the scene of the accident.

Investigators presumed the 51-year-old man had been killed when his truck collided with a four-wheel drive on the Glenelg Highway near Tarrington, in Victoria's west, about 6am Tuesday.

The scene of the fatal crash on the Glenelg Highway at Tarrington. Credit:Rob Gunstone

The 26-year-old South Australian man driving the 4WD died at the scene, east of Hamilton, and his 17-year-old male passenger was flown to The Royal Melbourne Hospital, where he is fighting for his life.

The prime mover burst into flames and police believed the driver's body was trapped inside its charred wreckage.