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 epicenter of the quake, which occurred at 0858 GMT, was located 102 kilometers (63 miles) west of Craig, Alaska at a depth of nine kilometers (5.5 miles), according to the USGS.

There were no immediate reports of casualties or damage.

The Pacific Tsunami Warning Center said there was no widespread threat of a tsunami at this time, but it issued a regional warning affecting the Alaskan coast near the epicenter.

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.

A similar 7.7-magnitude earthquake hit Canada's Queen Charlotte Islands, located just south of the current epicenter, last October. That quake did trigger a small Pacific tsunami which eventually reached the US state of Hawaii without causing any damage.