An earthquake of 7.5-magnitude struck in the Pacific Ocean about 100km off the coast of Alaska, the US Geological Survey (USGS) has said.

The quake struck on Saturday at a depth of about 10km at 0858 GMT, the survey said. The epicenter of the quake was located 106km west of Craig, Alaska, according to the USGS.

There were no reports of casualties or damage and a tsunami warning that was initially issued was later canceled for Alaska and Canada.

Earlier, the Pacific Tsunami Warning Center said that a local but possibly destructive tsunami was generated by the quake.

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

The Alaska Tsunami Warning Center said the warning area included coastal areas from about 120km southeast of Cordova, Alaska, to the north tip of Vancouver Island, Canada. The warning area extended for about 764km.

An earlier 7.7-magnitude reading of the quake was later adjusted to 7.5-magnitude 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.