The B-double log truck heading north left the Hamilton Highway just at 7.20am.

The driver was treated by paramedics at the scene but died.

South-west police road safety manager Senior Sergeant Chris Asenjo said the B-double was heading north out of Penshurst when the accident happened.

He said the truck and trailers ran off the road, crashed through trees and finished in a paddock.

"The primary focus of the incident at this stage is whether it involved a medical episode," he said.

"The initial advice we have received is that appears likely. We will have to wait for the autopsy report.

"An assessment of the scene indicates a medical episode will be a firm avenue of inquiry."

Senior Sergeant Asenjo said the truck remained upright, there was minimal damage to the vehicle and the driver had not suffered visible physical injuries.

"Clearly at this early stage we can't rule anything out, but an avenue of inquiry will be the state of the driver's health and if he had any health concerns," he said.

"As part of those investigations we will be seeking access to his medical records."

The road safety advisor said if the driver's death was due to a medical episode he would not count towards the state's road toll.

"But, a life has been lost and we acknowledge a tragic incident has occurred," Senior Sergeant Asenjo said.

"A number of road policing criteria have to be met before a life is counted towards the road toll," he said.

At 2pm: A 38-year-old log truck driver from Elliminyt died following a single-vehicle crash near Penshurst on Thursday morning.

The B-double log truck left the Hamilton Highway just after 7am before crashing through trees and coming to stop in a paddock.

He was treated by paramedics at the accident scene but died.

The investigation into the exact cause of the accident remains ongoing and will be headed by the Victoria Police major collision investigation unit members.

The Hamilton Highway has been closed north-west bound between Penshurst and Hamilton since soon after the accident and will remain so until further notice.

Police are asking motorists to avoid the area.

Anyone with information, who witnessed the incident or who may have dash cam footage, is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au

At 10am: The 38-year-old driver of a log truck which was involved in a single-vehicle accident just north of Penshurst this morning has died at the scene.

Paramedics worked on the man but it has been confirmed he has passed away.

Victoria police major collision unit members are in charge of the investigation into the cause of the accident.

Earlier: The HEMS4 rescue helicopter has been called in after a log truck went off the road and crashed into a tree on the Hamilton side of Penshurst this morning.

Police Sergeant Ray Hastings said emergency services were alerted at 7.20am.

The accident happened between Cemetery Lane and Batesworth Lane on the Hamilton Highway north of Penshurst.

The driver of the truck is believed to have suffered serious life-threatening injuries.

The highway is blocked and expected to remain so for some time.

VicRoads has issued a traffic alert saying the Hamilton Highway is closed at Batesford Lane north-west of Penshurst due to a serious collision.

Emergency services are setting up diversions and currently directing traffic.

"Please use Penshurst-Dunkeld Road and Hamilton-Chatsworth Road around the closure. Allow extra time," a spokesman said.

For the latest traffic information around the state visit traffic.vicroads.vic.gov.au or download the VicTraffic app via your app store.

More to come.

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