Portland police Sergeant Sean Elliott said the fatality happened at 10.20pm when a black Ford travelling east along the Portland-Nelson Road with two men onboard left the road and crashed.

He said the driver lost control, over-corrected and crashed into a fence.

The damage to the vehicle was almost exclusively to the driver's side and the driver died before emergency service attended the accident scene.

The passenger was not physically injured.

Sergeant Elliott said the weather conditions were described as foggy and raining at the time of the accident.

"At this stage there are no suspicious circumstances. The driver appears to have lost control, over-corrected and there was an accident in a 100km/h zone," he said.

"The impact has been to the driver's side and has resulted in the death of the 39-year-old driver. The passenger does not have a scratch," he said.

The exact cause of the accident is being investigated although it is understood that the driver’s side collided heavily with a fence post. 

The road toll for 2016 is 122, 17 more than for the same period last year.