An entire building has quietly vanished from the United States' mysterious Area 51.

Before and after photographs of the top-secret military base in the Nevada desert show a large hangar has vanished.

The mystery around the site has sparked rumours aliens and UFO have been captured there, as American authorities reveal almost nothing publicly about what its purpose is.

Long-range photographs captured by private pilot Gabe Zeifman offer a rare insight into the layout of one of the most enigmatic landmarks in the world.

The pilot had permission to fly along the border of the base despite the airspace over Area 51 being tightly restricted.

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