A 24-year-old woman is in hospital with life-threatening injuries after a long piece of metal — which police believe came from a tow truck — struck the windshield of a vehicle driving on Highway 401.

Police say at about 8:30 p.m. Tuesday a piece of metal more than two metres long was spotted in the eastbound lanes of Highway 401 west of Rougemount Drive in Pickering.

At least three vehicles struck the debris, resulting in deflated tires and minor damage.

A short time later the piece of metal came through the windshield of a vehicle, seriously injuring its driver.

Police say the item appears to be a "component used by tow truck operators to tow vehicles."

The driver of this car is in life-threatening condition after a two-metre long piece of metal pierced the windshield of this car on Highway 401 in Pickering. (Trevor Dunn/CBC)

Tow truck driver Eric Swackhammer says it looks to be one half of an aluminum dolly bar, which are used to secure the tires of towed vehicles.

The extendable bars go "width-wise across the car. They sandwich the tire, and they go right underneath the vehicle to the next tire," he told CBC News.

The equipment is meant to be well-secured on trucks. If it isn't, drivers can be fined by the Ministry of Transportation.

"We got quite a few inspections and stuff. MTO is always on us for keeping stuff secure on our truck," Swackhammer said.

OPP spokesperson Sgt. Kerry Schmidt says police want to talk to motorists, including tow truck drivers, who were in the area at the time.

"It doesn't matter if you're a tow truck, a passenger vehicle or a large transport truck, everything on your vehicle needs to be properly secured," he said.

Police are asking anyone with information to come forward and speak with investigators at the Whitby OPP detachment at 905-668-3388.