Video filmed by Jennifer Sonne, a local resident, showed tsunami warning sirens blaring in the city of Kodiak.
The U.S. Geological Survey (USGS) said the quake, which struck at 10:15 p.m. local time (0615 GMT Thursday), was at a depth of 35 km.
The quake reportedly struck about 91 km east-southeast of Perryville in Alaska. It was about 500 miles from Anchorage, Alaska's biggest city.
It was followed by seven aftershocks, two of them above magnitude 6.0, according to USGS.