The express lanes of Highway 401 have re-opened after a five-vehicle crash caused a major closure to both east and westbound lanes between Allen Road and Highway 404.

Paramedics were called to the scene of the crash in the westbound lanes of Highway 401 at Yonge Street around 12:30 a.m. on Thursday.

It involved five vehicles, including three transport trucks, OPP Sgt. Kerry Schmidt said.

"It looks like it was an end-of-queue crash," Schmidt told CBC Toronto, explaining that a transport truck had crashed into stopped traffic on the highway.

One man in his 40s and a second person of undetermined age and gender were taken to a trauma centre with serious, but non-life-threatening injuries, according to paramedics. A third person was also taken to hospital as a precaution.

No charges have been laid, said Schmidt, but the crash caused "a huge mess for clean up and traffic."

At the scene of the crash, the trailer of a truck was sitting across the westbound lanes, while the cab had jumped over the median into the eastbound lanes.

The cab of a tractor-trailer sits on the eastbound side of Highway 401 at Yonge Street, while the back half remains in the westbound lanes. (Tony Smyth/CBC)

"It was a bit of a blur because there was a lot of sparks and stuff flying," remembered witness Imran Habib, describing what he saw when he said a tractor-trailer "plowed through" a vehicle during the crash.

"I was telling the people in the vehicle, because they were conscious, I said you guys are very lucky you know," he said.

Imran Habib describes the moment a tractor-trailer crashed into a vehicle on Highway 401. (Tony Smyth/CBC)

According to Habib, the driver of the tractor-trailer was trapped in the cab, and another man was trapped in the car that had been hit.

"It's quite stunning, astonishing... I'm happy if everybody's good and everybody's alive, that's all you can wish and pray for."