Traffic was gridlocked on the eastbound lanes of Highway 401 in Milton on Thursday afternoon after a flatbed tractor-trailer lost control and knocked down a 33-metre light tower.

The truck, which was not carrying a load, crashed near Highway 407 just after 1:15 p.m.

Witnesses told police the vehicle began to waver, and then drove off the road and struck the massive tower, bringing it down.

The truck erupted into "a ball of fire," and the force of the impact knocked the cab right off the truck, said OPP Sgt. Cam Woolley.

The driver of the truck was taken to hospital, but escaped with non-life-threatening injuries.

All eastbound lanes in the area were closed initially, but police reopened all but two lanes just before 3 p.m.

The cause of the crash isn't yet known.

Police said speed was not a factor in the crash, but investigators would like witnesses to call them.