A major 7.7 magnitude earthquake shook the Queen Charlotte Islands off the west coast of Canada, US government researchers said. The epicenter of the tremor, which occurred at 8:04 pm (0304 GMT Sunday) was located 139 kilometers (86 miles) south of the town of Masset, the US Geological Survey said. Numerous aftershocks, some as large as magnitude 4.6, followed the initial quake, Canadian officials reported. The Pacific Tsunami Warning Center said there was no "destructive widespread tsunami threat" at this time. However, the regional West Coast-Alaska Tsunami Warning Center issued a regional warning for coasts located near the epicenter of the earthquake. Emergency officials in British Columbia said a small tsunami had been recorded on a deep ocean pressure sensor, but its effect was not immediately known. The officials urged residents in low-lying coastal areas to be alert to instructions from local officials and be prepared to move to higher ground. Natural Resources Canada said in a statement that the temblor was felt across much of north-central British Columbia, including Haida Gwaii as the Queen Charlotte Islands are otherwise called, Prince Rupert, Quesnel, and Houston. "There have been no reports of damage at this time," the ministry added. However, experts said tremors exceeding magnitude 7.0 were extremely dangerous. "A 7.7 is a big, hefty earthquake. It's not something you can ignore," Gerard Fryer, senior geophysicist at the Pacific Tsunami Warning Center told n CNN International. He explained that the latest tremor had occurred partly under an island, but mostly under shallow water. "I think we have to be thankful it happened where it did," Fryer said. "If that were a heavily populated area, it would have caused significant damage." "It definitely would have done significant damage if it had been under a city," the geophysicist added. The Globe and Mail newspaper reported that the US Coast Guard in Alaska was trying to warn everyone with a boat on the water to prepare for a potential tsunami, the report said. The Canadian paper also quoted Lieutenant Bernard Auth of the Juneau Command Center as saying that the US Coast Guard was working with local authorities to alert people in coastal towns to take precautions. The earthquake reading was based on the open-ended Moment Magnitude scale used by US seismologists, which measures the area of the fault that ruptured and the total energy released. The Queen Charlotte Islands, which are also known by their official indigenous name of Haida Gwaii, comprise about 150 islands located north of Canada's Vancouver Island. Their total population is about 5,000. The Haida people make up about 45 percent of the total population.