Senior Constable Ben Carroll, of the Hamilton police highway patrol unit, said the Melbourne driver had veered into the truck's path for unknown reasons.

The four-wheel-drive was heading east towards Dunkeld when the accident happened between the town and the intersection of the Glenelg Highway with the Dunkeld-Penshurst and Cavendish-Dunkeld Road.

The truck and trailer had nothing on the wide load trailer but was accompanied by front and rear pilot vehicles.

"The truck driver has tried to take evasive action but been unable to avoid the collision," Senior Constable Carroll said.

UPDATE, Thursday morning: The condition of the two elderly Melbourne women involved in the fatal head-on collision with a truck near Dunkeld on Wednesday continues to improve.

A spokeswoman for The Alfred Hospital in Melbourne said one of the women was now stable, while the other 80-year-old female was serious but stable.

WEDNESDAY: An 85-year-old Melbourne male driver has died and two female passengers flown to Melbourne after a head-on collision with a truck on the Glenelg Highway near Dunkeld.

The women, in their 80s and also from Melbourne, are listed as serious but in a stable condition after they were rushed by helicopter to Melbourne's The Alfred hospital.

One of the two women in the four-wheel-drive was believed to have been the man's wife.

A police spokesman said the accident happened between the Glenelg Highway intersection with the Dunkeld-Penshurst Road and the Cavendish-Dunkeld Road and the Dunkeld township.

It occurred on a straight stretch of road at the foot of Mount Sturgeon.

The middle-aged truck driver stopped at the scene and assisted police with their inquiries. He was not injured.

The police spokesman said the highway was blocked just west of Dunkeld between the Mount Sturgeon car park and the Dunkeld-Cavendish Road.

The Penshurst-Dunkeld Road remained open and traffic was diverted around the accident scene.

Police are investigating the cause of the collision

"It's a head-on collision. I'm not going into the cause of the accident any more than that," the police spokesman said.

Investigations into the cause of the accident will be carried out by the Hamilton police highway patrol unit members and Victoria Police major collision unit officers.

Anyone who witnessed or with any dashcam footage is asked to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au

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