An Associated Press reporter working in downtown Anchorage saw cracks in a 2-story building after the quake. It was unclear whether there were injuries.
People went back inside buildings after the earthquake but a smaller aftershock a short time later sent them running back into the streets again.
Shortly after the quake, a tsunami warning was issued for the southern Alaska coastal areas of Cook’s Inlet and part of the Kenai peninsula.
The warning means tsunami waves were expected.
The U.S. Geological Survey initially said it was a 6.7 magnitude earthquake and then reduced the magnitude to 6.6.