Several students in St. Paul were injured - including three who had to be flown to hospital in Edmonton with serious injuries - after a vehicle crashed into a school Thursday morning. The driver of the vehicle has been taken into custody.

RCMP said the 46-year-old male driver of a minivan went off the road and drove into the side of Racette Jr. High School in St. Paul around 9:30 a.m. Thursday.

Police say the vehicle went through the walls of a Grade 6 classroom and that three students received serious injuries after being pinned beneath the minivan.

"We were in class and all of you sudden you hear a big 'boom' and our school went under lock down," said Sage Nooskey, a Grade 9 student.

"Everyone is worried. We're just praying for them."

Police say all three children who were pinned under the vehicle were airlifted to hospital in Edmonton.

Cam Heke with STARS air amublance said the patient STARS airflifted was an 11-year-old girl.

She was taken to the Stollery in critical condition with life-threatening injuries.

By late afternoon Thursday, one of the three critically-injured students who were flown to hospital in Edmonton had been upgraded to being in stable condition.

Kerry Williamson with Alberta Health Services said five other people were taken to hospital in St. Paul with minor injuries and three were later discharged.

"We're shaken. All of our concerns right now are with the students," said District Supt. Glen Brodziak.

"Our thoughts and our prayers are with the children, their families and their communities."

RCMP say the driver of the vehicle, a St. Paul resident, received minor injuries.

"Upon responding to the scene, members took into custody a 46-year-old male and immediately commenced their investigation into this accident. I can say right now that the male is at the hospital right now, under treatment," said C. Supt. Randy McGinnis, RCMP district commander.

Police say the driver was 'combative' when he was arrested at the scene.

A police investigation is underway to determine what caused the man to go off the road and crash through a fence, field and into the classroom.

The RCMP Criminal Crash Investigation Team is overseeing the investigation. The team will work to determine whether drugs, alcohol, mechanical failure, road and weather conditions or medical conditions of the driver were causes of the crash.

"There are various aspects to this investigation that we are looking at and ruling in or out, one would be impairment, impairment by alcohol or a drug," McGinnis said.

Witnesses tell CTV News the minivan appeared to be travelling at a high rate of speed down an alley directly towards the school.

The vehicle somehow spun and ended up backwards inside the school.

Mike Vanderhoek witnessed the aftermath of the crash and described the scene to CTV News.

"They had the whole street blocked off, they are keeping people pretty far away," Vanderhoek said.

"STARS was in St. Paul so everyone was kind of worried, a lot of the town was checking it out. It's a pretty small community so they had it all taped off and you can see that it went right through the window, it missed the struts and everything, it went straight through the glass."

Police are asking anyone with information to contact 780-645-8870 or Crime Stoppers at 1-800-222-8477.

The school will remain closed on Friday. It's unclear when students will return to class.

St. Paul is located about 200 kilometres northeast of Edmonton.

With files from Bill Fortier