A powerful magnitude 7.9 earthquake struck off the coast of Alaska late Monday night, initially prompting a tsunami warning for a large section of the state's coast and parts of Canada. As more data came in, the U.S. Tsunami Warning System downgraded the threat to an advisory for Alaska's Chignik Bay.

Several smaller aftershocks were also felt after the quake, whose epicenter was located about 6 miles below the surface and 175 miles southeast of Kodiak, according to the U.S. Geological Survey.

Warnings from the National Weather Service were pushed out to cellphones in Alaska, saying: "Emergency Alert. Tsunami danger on the coast. Go to high ground or move inland."

But as the effects of the quake became clear, those alerts were soon canceled.

"The warning system reported several waves around the state of under a foot," member station KTOO reports.

In its initial response, , issued a tsunami warnings or watches for long swaths of the west coast of Canada and the U.S., from Alaska and British Columbia to parts of California. Public radio station in Kodiak issued this advisory over its airwaves: "This is a tsunami warning. This is not a drill. Please get out to higher ground."

In Sitka, Alaska, east of the quake's epicenter, schools that had been opened as shelters during the tsunami warning were later given the all-clear.

Reporter Emily Kwong of Raven Radio said via Twitter:

"Chimes going off in Sitka, Alaska, as booming emergency voice sounds the all clear: 'Repeat. The tsunami warning has been canceled. It is safe to return to coastal areas.' City says school will happen today. Kids I've spoken with have mixed feelings about that."

There were no immediate reports of damage or injuries related to the earthquake.

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