A 6.1 magnitude earthquake struck off the northwest coast of Vancouver Island at 1:19 p.m. PT Tuesday, followed by a series of at least five aftershocks, but officials say no tsunami is expected.

The U.S. National Oceanic and Atmospheric Administration's National Weather Service was the first to report the quake's epicentre was approximately 150 kilometres northwest of Port Alice, on Vancouver Island, but said a tsunami was not expected.

The quake was initially rated 6.2 magnitude by the NOAA, but then downgraded to 6.0 by the USGS, while Natural Resources Canada rated the quake 6.1 magnitude.

NRC seismologist Alison Bird says there is no cause for concern because the quake was out in the ocean rather than underneath people.

"I would consider this to be a moderate earthquake. It doesn't pose any threat to people. There is no tsunami expected. We haven't even received any fault reports yet. It's far enough away from communities that it really isn't any worry," said Bird.

Residents in Bella Bella, Port Alice and Port Hardy contacted by CBC News said they did not feel the quake or its aftershocks, but Bird says it is a reminder folks should take part in the provincewide Shakeout B.C. earthquake drill next month.

Aftershocks recorded

At least five aftershocks were reported in the same area including a 4.6 magnitude at 2:05 p.m, a 4.8 magnitude at 2:25 p.m., a 5.0 magnitude at 3:29., 4.2 magnitude at 4:07, and 5.9 magnitude at 5:23 p.m.

"The earthquakes had 'strike-slip' mechanisms which means the motion was mainly horizontal," said CBC meteorologist Johanna Wagstaffe, who has a background in seismology.

"Here, two plates are sliding past each other, rather than one plate moving underneath another one. These quakes are likely connected to the Queen Charlotte fault rather than the Cascadia subduction zone, but this is a complicated section of West Coast tectonics. It's possible these quakes are connected to last year's October 2012 7.8 magnitude quake as well."

The area of the ocean floor west and north of B.C., often referred to as the Pacific Ring of Fire, is known for its seismic activity.

On Tuesday evening, a magnitude 6.5 earthquake struck near the Izu Islands in southern Japan. Tremors were felt in Tokyo, but no damage was reported and no tsunami expected. The Japan quake was not connected to the B.C. quakes.

On Monday, a much smaller 3.9 magnitude earthquake registered approximately 119 kilometres southwest of Port Alice, according to Natural Resources Canada.

Farther to the northwest, a 7.0 quake last week shook near the coast of Adak, one of Alaska's Aleutian Islands.