Police say the exact details of the fatal crash are yet to be determined but they have been told the trailer detached from the truck cabin, veering into oncoming traffic.

The driver of the ute, aged in his 60s, was the sole occupant and died at the scene.

Assistant Commissioner for road safety Doug Fryer told 3AW it was the 11th fatal truck crash this year, up on last year's figures.

"It's a really tragic set of circumstances," Assistant Commissioner Fryer said.

The truck driver is assisting police and an investigation is ongoing.

The Glenelg Highway was closed from Winter Street to Racecourse Road in both directions. VicRoads said truck drivers in the area were being turned around and asked that other drivers delay their travel or seek an alternative route.

Anyone who witnessed the crash is urged to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppersvic.com.au.

Victoria's road toll is 58 lives lost this year, compared to 79 last year.

UPDATE, 8.50am: Victoria Police confirmed a man has died following a collision near Coleraine on Thursday morning.

 It is believed a truck was travelling along the Glenelg Highway, east of Coleraine about 7am, when its trailer detached from the prime mover.

 The trailer then veered onto the other side of the road, colliding with an oncoming utility.

 A man in his 60s, who was the sole occupant of the ute, died at the scene.

 The truck driver is assisting police with their inquiries.

 The exact circumstances of the crash are yet to be determined and the investigation is ongoing.

 Anyone who witnessed the crash is urged to contact Crime Stoppers on 1800 333 000.

Friday, 8.20am: Traffic is being diverted onto a dirt road, a motorist on route to Casterton told The Standard.

"I had to wait for about 10 minutes," she said.

A police officer advised the motorist, who was behind about six trucks, of the incident.

"All I can tell you is there is an accident up ahead," the officer said.

Friday, 8.15am: The fatal accident happened on the steep hill along the Glenelg Highway on the east side of Coleraine.

There was a single vehicle rollover on March 21 along the same stretch of road, near Racecourse Road, but the driver did not suffer significant injuries.

Heavy haulage is currently being called in, Victoria Police’s major collision investigation unit has been notified and traffic is being diverted.

There was a fatal single-vehicle accident overnight last Thursday at Warrock, north of Casterton.

A red ute was travelling south along Casterton-Apsley Road when it hit a tree.

On Tuesday this week a motorcyclist lost his life at Culla near Harrow while riding south on the Coleraine-Edenhope Road after colliding with a tree.

Thursday, 7.52am: There has been a fatal accident near Coleraine on Thursday morning involving a truck.

The accident happen about 7am.

Emergency services have or are attending the accident scene.

Details are sketchy but it has been confirmed one person has lost their life.

Police have called for back-up to assist with traffic.

It is expected that there will be a major disruption to traffic in the area.