A "strong" underwater earthquake occurred off the coast of B.C. early Saturday morning, registering a magnitude of 6.7.

The quake, the second of three to strike in the same area early this morning, hit at about 3:45 a.m. Pacific Standard Time Saturday, said Guy Urban of the West Coast and Alaska Tsunami Warning Center.

The original quake had a preliminary magnitude of 5.3, Urban told CTV Newsnet. 

"We thought nothing of it, put out an information statement on it, and approximately 20 minutes later the larger quake came in with a preliminary magnitude of 6.7, and that was located almost in the same spot about 135 miles (241 kilometres) southwest of Sandspit, Queen Charlotte Islands."

Urban said there is little or no chance of a tsunami occurring, but officials followed standard procedure and released a "tsunami information statement high" to make people aware that a quake had taken place.

"A damaging tsunami IS NOT expected along the California, Oregon, Washington, British Columbia, and Alaska coasts," says the statement from the centre. "Some of these areas may experience non-damaging sea level changes. At coastal locations which have experienced strong ground shaking, local tsunamis are possible due to underwater landslides."

The underwater quake registering a magnitude of 6.7 could easily cause major damage were it to occur on land, Urban said.

"It would probably cause walls to crack and probably concrete foundations to tumble a little bit, so it could be fairly devastating. It's called a strong earthquake so it's large enough to cause some damage."

Urban said underwater earthquakes of 30 seconds or more have the potential to cause a tsunami.

"The general rule of thumb is if people are in or near the water when an earthquake occurs and it lasts for more than 30 seconds they should go to high ground because there's a possibility a tsunami could have been generated."