A strong 7.7-magnitude earthquake shook the Queen Charlotte Islands off the west coast of Canada today, US government researchers said.

The epicentre of the tremor, which occurred at 8:04 local time (0304 GMT) was located 139 km (86 miles) south of the town of Masset, the US Geological Survey said.

The Pacific Tsunami Warning Centre said there was no threat of a tsunami at this time.

There were no immediate reports of casualties or damage.

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.

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