A man involved in a highway crash Tuesday morning is in serious condition in hospital after his car hit tires that had come off a garbage truck.

Three other cars were involved in the accident, which happened at 4:30 a.m. ET Tuesday on a dark stretch of Highway 403 near Dundas.

Police say the vehicles collided with a pair of runaway tires that came off a Rexdale Disposal truck.

Of the four crashes, the most serious involved a Subaru sedan. The 23-year-old driver was thrown from the car and air-lifted to hospital with serious head injuries.

Transport truck driver Desmond Lumzel was on the scene of that crash and helped the injured driver.

"All I hear is crunch and then another car hit the tire," said Lumzel. "And he started to flip. He started to roll over and as I heard all that, I was calling 911. From what I can see, he was bleeding from his head and holding his stomach."

Police said two wheels from the same truck came off on the highway and were impossible for drivers to see in the darkness.

"The first wheel came off right [and the truck] continued down the roadway," said OPP Const. Graham Williamson. "And another two vehicles struck the second wheel that was in the roadway."

The province introduced stiffer fines for trucking companies responsible for runaway wheels after a number of fatal incidents a decade ago. Companies found liable in cases of wheel separation can face fines of up to $50,000.

"There's a reason the province fines you $50,000 for this kind of incident," said Brian Patterson of the Ontario Safety League. "Because it is preventable and it can kill people."

A spokesperson for Rexdale Disposal told CBC's Genevieve Tomney he was very concerned about the accident but wouldn't comment on what happened because he hadn't seen the vehicle.

With files from CBC's Genevieve Tomney