EVER since the 1950s, the US government's Area 51 - located deep within the remote Nevada desert - has been the subject of intense conspiracy theories.

But now Google Maps has offered a rare glimpse of the mysterious government site - revealing a massive build up of infrastructure at the base over the past 30 years.

5 Area 51 pictured from above in 1984 Credit: Google Maps

5 By 1990 another runway appears to have been constructed Credit: Google Maps

5 And in 2007, more buildings can be seen built into the neighbouring mountain Credit: Google Maps

5 Here it is seen in 2016 - revealing a swathe of new infrastructure Credit: Google Maps

Satellite imagery recorded annually since 1984 shows a rapid expansion of buildings and runways at the base.

This includes the construction of a second runway and what appears to be an extension of the first.

Buildings are also being constructed into the side of a nearby mountain - though what they contain remains a mystery.

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While the existence of Area 51 is common knowledge, for decades the US refused to even acknowledge its existence.

The base and the area surrounding it are entirely off-limits for civilians, while the airspace is a no-fly zone.

Military personnel with weapons patrol the perimeter of Area 51, with signs warning that security can use "deadly force".

The closely-guarded nature of Area 51 adds to the intrigue of a site long associated with UFO conspiracy theories.

The US Air Force Base, around 80 miles from Las Vegas, is thought to be used for the development and testing of experimental aircraft.

Many conspiracy theorists claim that the base has been used for reverse engineering of an alleged crashed alien spacecraft at Roswell.

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