WASHINGTON: A major 7.7-magnitude earthquake shook an area in the Pacific Ocean off the coast of the US state of Alaska early Saturday, the United States Geological Survey said.

The epicentre of the quake, which occurred at 0858 GMT, was located 102 kilometres west of Craig, Alaska, according to the USGS.

There were no immediate reports of casualties or damage.

The Pacific Tsunami Warning Centre said there was no widespread threat of a tsunami at this time, but it issued a regional warning affecting the Alaskan coast in the proximity of the epicentre.

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.