Up to 100 people have been transported to hospital after a highway crash involving 100 vehicles in Edmonton on Thursday afternoon.

According to the RCMP, a bus, tractor trailer units and some trucks and small cars collided at about 11:30 a.m. Thursday on Highway 2 -- the main road between Edmonton and Calgary. Police said an initial crash caused a chain reaction.

Alberta Health Services initially said in a tweet that 300 “minor to moderate injuries” had been reported. In a later update, AHS spokesperson Kerry Williamson said 100 patients were transported to 10 area hospitals with injuries running the "gamut from minor to serious."

One person with serious injuries was taken to the University of Alberta Hospital.

The service said it had the capacity to treat the injured with hospitals in Edmonton, Red Deer, Leduc, St. Albert, Fort Saskatchewan, Devon, Wetaskiwin, Stony Plain, Lamont and Camrose accepting patients.

Some patients with minor injuries were being assessed on three Greyhound buses, AHS said.

Derek Fildebrandt , who witnessed the crash while riding in a coach told CTV Edmonton, “It was a pretty massive pileup, far bigger than I’ve ever seen before. From what I could see there were remarkably few injuries considering the scope of the accident.”

Authorities closed the major highway in both directions. It's not expected to open until late Thursday night or the early hours of Friday morning.

By Thursday evening, southbound traffic on the QE2 highway was being diverted while officials sifted through evidence at the crash scene.

Although the investigation is still ongoing, police said speed was likely a factor in the collision.

With a report from CTV Edmonton