A number of tsunami warnings were downgraded to advisories late Saturday after a 7.7-magnitude earthquake struck off the coast of British Columbia.

A tsunami warning was downgraded to an advisory for a coastal area from the north tip of Vancouver Island to Cape Decision, Alaska, according to a bulletin issued at 11:17 p.m.. PT by the U.S. National Weather Service’s West Coast/Alaska Tsunami Warning Center.

Advisories remained in effect for a region stretching from the Washington-B.C. border to the north tip of Vancouver Island, and for coastal areas of Washington, Oregon and California.

The agency said that “a tsunami has been generated,” which was expected to impact low-lying areas covered by the advisories. The agency advised residents to watch for instructions from local emergency officials.

  • “A tsunami advisory means that a tsunami is capable of producing strong currents or waves dangerous to people in or very near the water is expected,” a bulletin issued just before midnight said.
  • “Significant widespread inundation is not expected for areas under an advisory.”
  • The bulletin said currents that may pose a hazard to swimmers, boats and coastal structures “may continue for several hours after the initial wave arrival.”

A tsunami warning remained in effect for Hawaii.

“A tsunami has been generated that could cause damage along coastlines of all islands in the state of Hawaii,” the agency said. “Urgent action should be taken to protect lives and property.”

Earlier Saturday, the agency had warned that, “Those feeling the earth shake, seeing unusual wave action or the water level rising or receding may have only a few minutes before the tsunami arrival and should move immediately.”

A tsunami had been forecast to hit Langara Island, at the northern tip of Haida Gwaii, around 9:16 p.m. PT. However, Emergency Info BC tweeted shortly before 11 p.m. PT that two waves under 50 cm were recorded in the region. Later, a 12 cm wave was reported in Tofino, on Vancouver Island.

The agency said that a warning means a tsunami is “expected and imminent” in low-lying coastal areas, and residents should move inland or to higher ground immediately. An advisory indicates that a low-level tsunami is expected. Residents under a tsunami advisory are being told to stay away from beaches and shorelines “until further notice.”

The U.S. Geological Survey said the quake struck just after 8 p.m. local time about 139 km south of Masset in the Haida Gwaii region, at a depth of about 17 kilometres.

Earthquakes Canada, which initially gave the quake a magnitude of 7.1, said the quake was felt across much of north-central B.C.

The quake was followed by eight aftershocks, the first one being the strongest at a magnitude of 5.8, the USGS said.

There were no immediate reports of injuries or damage.

Some power knocked out

Local resident Geoff Ray told CTV that he was concerned for his home because of the violent shaking, which knocked the power out.

“It was pretty intense right from the get-go,” he said.

The quake triggered a tsunami warning from Environment Canada, which advised residents to seek higher ground or move inland.

“Do not return until directed to do so,” the agency said. “Closely monitor local radio stations for additional information from local authorities.”

CTV British Columbia’s Penny Daflos reported that some low-lying communities, including Sandspit, Bella Bella and Prince Rupert, were being evacuated as a precaution.

B.C. Premier Christy Clark took to Twitter late Saturday to say “the province is prepared to respond as needed.”

Bruce Presgrave of the USGS said a tsunami warning “is pretty much standard procedure” after a 7.7-magnitude quake.

A tsunami could do more damage to the region than the quake itself, he told CTV News.

“A 7.7 is a strong earthquake, capable of producing significant damage or casualties in populated areas,” Presgrave said.

“But as I’m sure you folks know, Haida Gwaii itself is pretty sparsely populated. And even though the West Coast of northern British Columbia there is fairly sparsely populated, the biggest risk could be if a tsunami has been generated.”

According to the USGS, seven earthquakes of magnitude 6 or greater have hit the region in the past 40 years. The biggest over that period, until Saturday’s quake, measured 6.6 magnitude.

An earthquake of magnitude 8.1 hit the northern tip of Haida Gwaii in 1949.