A 56-year-old Toronto man is dead after a sedan collided with a loaded flatbed transport truck in the westbound lanes of Highway 401 near Martin Grove Road on Monday morning.

The "rear end-type crash" occurred around 5:20 a.m. in the northwest corner of the city, according to Ontario Provincial Police Sgt. Kerry Schmidt.

Just minutes before the fatal collision, two cars got into a minor crash in the middle lanes. One of the vehicles was able to make it to the shoulder, however the other driver remained stalled straddling two lanes. It is not clear at this point if the car was disabled or if the driver simply stayed parked on the highway, Schmidt explained.

Soon after the first crash, a fully-loaded flatbed transport truck hauling steel beams slammed into the back of the sedan in the road, killing 56-year-old Cristinel Murariu, Schmidt said.

The male driver was pronounced dead when paramedics arrived, while the truck driver was largely unhurt but "very shaken." He co-operated with police at the scene.

All of the westbound lanes of Highway 401 were closed, as well as the off ramp to Martin Grove Road, throughout the morning commute. The closure has since been cleared, Schmidt said, adding that the incident was "an absolutely devastating crash."

OPP Sgt. Kerry Schmidt said it was "an absolutely devastating" collision. (Tony Smyth/CBC)

The OPP's collision reconstruction unit is investigating the collision. Schmidt said that several witnesses have given statements to police, but added that officers would like to speak with several drivers who were supposedly at the scene of the crash earlier but then left.

He advised that drivers should do everything possible to get their vehicles off the road after an accident.

"If you ever have a breakdown, we really need you to get off the highway ... to avoid this type of situation from happening," he said.

The collision comes as the OPP prepares to begin a weeks-long transport truck safety blitz following a number of high-profile fatal crashes in recent months. Officers will be riding in unmarked transport trucks on 400 series highways so they can better observe other truck drivers, as well as cars driving dangerously around transports.

Schmidt commended the professionalism of Ontario's trucking industry, but added that those in the business are held to a higher safety standard than regular motorists.

"When somebody's not paying attention, that last car in line is really sitting there with no protection. And when it's a transport truck driver who's not paying attention, the weight of 80,000 pounds or more slamming into the back of stopped traffic is just completely devastating," he said.