A bizarre cloud over Alaska's Lazy Mountain sparked a probe following fears it could have been a Russian weapon or UFO.

Pictures of the mystery grey and while plume circulated on Facebook on Thursday, prompting some to believe it was aliens or a meteor.

The cloud gathered so much attention that Alaska State Paratroopers and the Alaska Rescue Coordination Center began investigation for a possible plane crash.

A chopper and rescue crew were sent out to survey the area but found "nothing suspicious... nor signs of crashed aircraft".

That didn't stop theories running wild online.

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