The epicenter was located 135 kilometers south-southeast of the town of Port Hardy on the island, the U.S. Geological Survey said in its assessment.
The USGS reported it was at a depth of 23 kilometres, revising its original assessment that it was only two kilometres below the surface.
A geophysicist with the U.S. Geological Survey said damage in many B.C. regions would be likely.
"It's been felt pretty widely — we have reports of it being felt in Vancouver, Victoria and even in Seattle," said Paul Caruso.
"We don't have any reports of damage yet, but we would probably expect to see some damage — especially for anybody living on the central-west coast of Vancouver Island."
There were no immediate signs of damage in downtown Vancouver. In the Vancouver Sun newsroom, lights swayed for a half-minute when the quake struck.
The earthquake shook buildings in the tiny Vancouver Island community of Zeballos, but there appeared to be no damage and there were no injuries.
The power went down but came back quickly, said Arlene Coburn, a 38-year resident of the remote west coast community.
Coburn was at the school when the earthquake hit. She said that it felt like the whole building was going to topple over, but nothing fell off the walls. "One big one, and a little tremor, and that was it," she said. "It gave [the school] a good sway."
The 60 or so children that attend the Zeballos Elementary Secondary School were ushered out and across a bridge, a measure used when there's a concern of a Tsunami, said Coburn, a part-time janitor at the school.
Arlene's husband Geoff said there were no injuries and no damage as far as he knew in the community of about 200 people. "There was no cause for panic," said Geoff.
The aboriginal community of Kyuquot on the outer west coast of Vancouver Island was shaken up as well, but there also appeared to be no structural damage and no injuries.
Jordan Lee, who manages the community's housing and water works, said he was talking to one of his crew members when the earthquake hit, causing a nearby work truck to shake. Two 70-foot mobile homes also really shook, said Lee. "Everybody in the community came out the doors."
A key concern was the danger of a Tsunami but no warning was issued, said Lee, noting the community has a plan to run to higher ground if a warning is issued.
The earthquake had a similar impact on the Village of Tahsis, shaking buildings but appearing to cause no damage. There were no injuries in the community of 300, said Sharon Taporowski, who works for the village.
The earthquake only lasted several seconds, coming in two quick waves, she said.
Brent Ward, a professor in Simon Fraser University's department of earth sciences, said people were more likely to feel the quake if they were in tall buildings because of the sway. He said this is one of the biggest quakes experienced on the west coast, with the last one in Washington. "6.7 (the quake's originally estimated magnitude) is nothing to sneeze at," he said. "You think of the earthquake in Haiti and it was about the same but it was shallow."
Ward said it's doubtful the quake will lead to a tsunami risk because it's too deep. He said the quake likely originated from stress built up due to the oceanic Juan de Fuca plate subducting under the North American plate.
The quake created a slight rattling as far away as Seattle, Washington, but police in the U.S. city said there were no reports of damage. The list of cities where the quake was felt includes San Francisco and Edmonton
Regardless, he said some residents will be directly effected by the earthquake.
"People might experience — if they're near the epicentre on the west coast of the island — they might have some damage, with things falling off shelves and cracked foundations," Caruso said. "As far as the mainland, we would probably expect to see very minor damage. People would probably see their chandeliers swinging back and forth and feeling a little bit of shaking."
TransLink spokesman Drew Snider said staff in Metrotower II in Burnaby experienced about three minutes of swaying and clanging blinds on the upper floors of the tower.
According to the Victoria Times Colonist, the largest quake in recent memory was the 6.8-magnitude Nisqually earthquake southwest of Seattle, Washington in February 2001.
Only the ninth earthquake in this area in 125 years measuring over magnitude 6, it cracked the dome of the Capitol building in Olympia, Washington, damaging the control tower at Sea-Tac airport and shook bricks off chimneys in Victoria.