The eastbound lanes of Highway 401 through Mississauga are expected to remain clogged throughout the afternoon following a crash involving a tractor trailer hauling pigs, the second recent accident involving livestock on a GTA road.

Monday morning's crash occurred near Winston Churchill Blvd. Ontario Provincial Police originally shut down all eastbound and westbound lanes, but then re-opened the westbound ones.

"About 8 a.m. this morning, Highway 401 eastbound was slowing down as it usually does in morning rush hour," OPP Sgt. Cam Woolley told CTV.ca Toronto.

"A tractor-trailer travelling eastbound, hauling livestock, for some reason failed to slow down and slammed into slower traffic, virtually crushing a full-sized pickup and ramming a car and a large van.

"The tractor-trailer then hurtled over to the left lane and rolled onto its right side, with the cab bursting into flames," he said.

"The driver escaped -- along with about 50 to 60 pigs."

The pickup truck driver suffered very serious injuries. The car driver was also injured, and the van and tractor trailer driver suffered minor injuries. All four were taken to hospital, Woolley said.

The eastbound lanes will likely stay closed until the early to mid-afternoon, he said.

Woolley told CTV Toronto it's a miracle anybody survived the crash.

"Had the big rig hit this Honda first, I really think it would not have been surviveable," he said. "The bigger vehicle absorbed most of the impact before the Honda was hit."

The escaped pigs scampered around on the highway or munched on grass beside the road. However, two pigs had to be euthanised at the scene.

But Woolley said most of pigs have been corralled now. A livestock truck has been commandeered to haul them away.

The truck driver will most likely face charges, police say.

On March 20, some cattle escaped after a crash near Highway 427 and the Queen Elizabeth Way. Police shot one of the animals after it became spooked and aggressive, but Woolley said the pigs were much calmer. 

With a report from CTV Toronto's Dana Levenson