One night in July, Const. Brian Griffith was responding to a call in Air-1, the Edmonton police helicopter, when he saw something flying near him.

At first he thought it was a bird, but on closer inspection he realized it was a high-flying drone, white with red lights and a rotor at each of its four corners.

"We were flying at about 180 kilometres an hour, 1,500 feet off the ground," Griffith said Friday.

"We had a very close encounter. By close I mean it was it was within 30 or 40 feet to the helicopter, which could be significant, possibly catastrophic, if we had collided with the drone."

Const. Brian Griffith has been a pilot with Edmonton police for two years. (CBC)

Griffith has been a pilot for Air-1 for two years. He said his encounter over downtown Edmonton at about 10 p.m. on July 8 was the closest the police helicopter has ever come to colliding with an unmanned aerial vehicle.

If a collision had happened, Griffith said, the impact would have been similar to hitting a large bird. At the speed the helicopter was travelling at, it could have been catastrophic.

"It would come through the windshield. It could incapacitate the pilot. The tactical officers are trained in the event that if the pilot is incapacitated they could land it, but it could significantly damage the aircraft," said Griffith.

If there is a catastrophic failure, we have to come down somewhere. - Const. Brian Griffith

Even if it didn't hit the windshield, it could have hit the tail rotor or been sucked into the engine, causing the helicopter to lose power in the air.

Both officers on board Air-1 are trained to land the helicopter without power. But if they are flying over the city, it would leave them in a dire situation, Griffith said.

"It could be fatal. More importantly … it's the citizens of Edmonton that are below us. If there is a catastrophic failure, we have to come down somewhere."

Transport Canada says drones are not to be flown near moving vehicles, highways, bridges and busy streets, or anywhere the devices could interfere with first responders.

People are legally required to keep their drones from flying higher than 90 metres above the ground.

Drones are only to be flown in daylight hours and no higher than 90 metres (300 feet) above the ground.

In the incident detailed Friday, the drone was flying far higher than the legal maximum.

"At 1,500 feet we wouldn't be expecting a drone to be operating at the altitude," he said.

Griffith said the drone was flying so high, there's a good chance the operator wasn't able to see it, a legal requirement.

Police are investigating. If caught, the culprits could face charges under the Criminal Code and the Aeronautics Act.

"We will look for the users and we are quite successful at finding them," said Griffith.

About 30 minutes after the July 8 close call, two other smaller drones were observed in the same area, police said.