Portland highway patrol police said the man in his 50s crashed on a straight stretch of the Princes Highway at Mumbannar, near the South Australian border, about 4pm.

Investigators believe a Holden utility was travelling west along the Princes Highway towards South Australia. 

It appears the driver lost control of the car and crashed into a tree. 

Acting Sergeant Andrew Dunlop said the driver was dead on arrival and his family had been notified.

The accident was the district’s second single-vehicle crash into a tree within 10 hours, after a 25-year-old Dartmoor man hit a tree west of Dartmoor and was taken to Mount Gambier hospital.

“I think fatigue seemed to play a role in both accidents,” Acting Sergeant Dunlop said.

“With the extreme weather conditions at the moment, both factors would be an influence.”

The Dartmoor man was taken to hospital with serious injuries after crashing into a tree on the Princes Highway about 7.45am on Monday. He was trapped inside his car for about an hour.