A major 7.5-magnitude earthquake shook an area in the Pacific Ocean off the coast of the US state of Alaska early Saturday, triggering a potentially destructive local tsunami, the US government 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 United States Geological Survey.

The strength of the tremor was initially put at 7.7, but it was later downgraded to 7.5. Several aftershocks measuring from 2.5 to 4.8 hit the area in the wake of the first one, the USGS said.

There were no immediate reports of casualties or damage.

But the Pacific Tsunami Warning Center said a local and possibly destructive tsunami has been generated by the quake.

"Sea level readings indicate a tsunami was generated," the US center said in a statement. "It may have been destructive along coasts near the earthquake epicenter."

It added that "no tsunami threat exists for other coastal areas in the Pacific, although some other areas may experience small non-destructive sea-level changes lasting up to several hours."

Homes were shaken in Alaska's state capital of Juneau some 205 miles (330 kilometers) away, The Juneau Empire newspaper reported. But there was apparently no major damage to the city, the largest in the area.

Juneau resident Archie Hinman told the Empire the quake "shook my Juneau home violently enough to awaken the entire family. No apparent 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.

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.