The company said the attack occurred at its oil sands base plant about 25km north of Fort McMurray in Alberta province with the worker pronounced dead at the scene.

"We are shocked by this very unusual incident and there are no words to express the tragedy of this situation," Suncor upstream executive vice president Mark Little said.

"Our thoughts and prayers go out to family, friends and co-workers. All of us need to focus on personal safety and I would urge everyone to be extremely vigilant in dealing with wildlife."

Fish and wildlife authorities put the animal down and an investigation into the event is underway.

While grizzly bears are considered more dangerous, Calgary news station CTV reported that it was a male black bear that fatally injured the undisclosed employee and it was not known if she was working alone at the time.

Last month a Suncor electrician died near electrical panels at one of its sites while another male employee was found dead in one of the company's sand dump areas in January with local media at the time reporting that this death did not appear to be suspicious.