A man has been flown to hospital in a critical condition after two trucks collided in what a witness said was a "disastrous scene" north-west of Melbourne.
The collision happened on the Western Freeway at Bacchus Marsh about 7:40am.
Police said it was believed one truck collided with the rear of the other, causing it to veer several hundred metres up the road before catching on fire.
One man, in his 50s, was treated for head injuries at the scene and flown to The Alfred Hospital in a critical condition.
He is now in a serious but stable condition, police said.
The other driver did not appear to be injured.
Witness Noel told ABC Radio Melbourne at first he heard an explosion, before passing the scene on his way to work.
"There were a couple of trucks that are close to disintegration," he said.
"There's many helicopters there, there's police, there's ambulances. It's a disastrous scene."
He said he had recently contacted authorities about dangers along the stretch of road, which is being upgraded.
"I actually called VicRoads about this [section of road]. They're putting in a second off-ramp on the Western Highway," he said.
"They basically have concrete bollards, unprotected concrete bollards, on the hard shoulder or almost on the side of the freeway.
"I called them to say this is an accident waiting to happen."
All Melbourne-bound lanes have been closed on the freeway near Bacchus Marsh Road.
