A tsunami warning issued for parts of Alaska's Aleutian Islands has been downgraded to an advisory.

The warning came after a magnitude 7.9 earthquake struck about 15 miles from Little Sitkin Island.

The quake generated small tsunamis, with waves of less than 7 inches, prompting the National Tsunami Warning Center to downgrade the warning, The Associated Press reported.

The quake had a depth of 71 miles and was expected to produce a "modest" tsunami, according to the Pacific Tsunami Warning Center.

There were no initial reports of damage in Adak or on Shemya Island, said Ian Dickson, website manager for the Alaska Earthquake Information Center.

Dickson said there were 17 measurable aftershocks in the two hours after the quake.

First estimates put the quake at magnitude 8.0, and prompted a tsunami warning. The strength was subsequently set by the U.S. Geological Survey at 7.9 magnitude and the tsunami warning was scaled back to an advisory.