A primer mover was parked on the roadside corner of the Glenelg Highway and Tarrington-Strathkel Road, just east of Hamilton, when its trailer ignited for unknown reasons just after 9am.

With CFA and police on site, the road was completely blocked until the fire was extinguished at 10.30am and traffic opened in one lane on the Glenelg Highway.

CFA operations officer Steve Giddens said seven fire units responded to the call due to the low water supply in the area.

"There was a really good response from our volunteers, a quick response again," he said.

"They saved a lot of damage to the truck, which was removed from the trailer and parked around the side by the driver."

Mr Giddens said firefighters used a breathing apparatus due to smoke in the area.

"A thermal imaging camera was used to detect heat inside the bin after the fire was out.

"The company is now organising removal of the potatoes.

"A heavy haulage crane will put them on another semi-trailer and they'll be removed from the scene."

He said appliances would remain on the scene until about noon while the trailer is removed.

VicRoads have been notified of the incident due to melting tar on the road shoulder.

There were no injuries to the driver or CFA volunteers at the scene.