An attack on a police officer outside a football game and a high-speed chase that injured four people in the western city of Edmonton are being investigated as acts of 'terrorism', Canadian police said on Sunday.

The chaos began outside a Canadian Football League game on Saturday night when police say a white Chevrolet Malibu rammed a traffic-control barricade and sent an officer flying five metres into the air.

Edmonton Police Chief Rod Knecht said the driver, believed to be 30-years-old, then got out and attacked the officer with a knife before fleeing on foot.

Knecht said an Islamic State of Iraq and the Levant (ISIL, also known as ISIS) flag was found in the front seat of the car.

The policeman was taken to a hospital and treated for non-life-threatening injuries while a manhunt was launched. "It's not critical," Knecht said.

He said he did not know the extent of the pedestrian injuries.

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A few hours later, a moving van was stopped at a police check-point north of the city. The vehicle then sped off with police in pursuit.

The van intentionally swerved at pedestrians at crosswalks throughout the chase. Four people were injured by the van, but the extent of their injuries was not immediately known.

Witness Kim Anderson was on the street waiting for a bus when the van began ramming into pedestrians.

"There were people flying and everything," she told the Edmonton Journal. "I'm shocked - I just see people flying."

Bar manager Austin Elgie also saw the van zoom by with police giving chase. "It was crazy. It just came around the corner, ripping."

Elgie said the van hit a man who was a customer.

"I have a registered nurse on my bar team and I grabbed her and had her look after the guy until the ambulance came," he said. "He was breathing and we got him in the ambulance and he was still breathing."



The van eventually rolled near a downtown hotel and a suspect was arrested.

Witness Pat Hannigan told reporters he saw police pull the man from the windshield of the toppled U-Haul van. He said 30 police cars were chasing the vehicle when it crashed.

Knecht said the assailant was known to police, but did not release his name.

"It is believed at this time that these two incidents are related," he said. "It was determined that these incidents are being investigated as acts of terrorism."

Knecht said one person is in custody and police believe he acted alone but are not ruling out others may be involved.