More than two million people said they would attend Saturday's "storming" of mysterious military base Area 51 — but when push came to shove, only 75 actually showed up.

Despite international interest in the event and literally millions of people promising they'd be there, only 1500 people had actually made the trek to the Nevada desert when festivities kicked off around 3am local time on September 20, reports News.com.au.

Of those, most gathered in remote nearby townships of Hiko and Rachel to attend alien-themed "festivals".

Lincoln County Sheriff Kerry Lee says only 150 people travelled closer to the mysterious base itself and just 75 actually approached the gates. Another group of 40 people gathered at a different gate.

They were a ragtag bunch, dressed in bright clothes, space suits and tin foil hats, and no actual 'storming' occurred, with some attendees only coming to witness what they thought would be some mayhem.

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Jason Strand, 23, told the ABC he travelled from Utah with nine friends "to see the dumb people make a run for it".

Wired reports police were "friendly and jovial" and even encouraged people to approach the gates, while The Independent says law enforcement approach others camped nearby, encouraging them to move on in a series of 'heated warnings'.

Only two arrests have been made, one woman who allegedly attempted to duck under Area 51's gates, and another, a man, for public urination.

The 'storming' was the brainchild of social media prankster Matty Roberts, who posted a Facebook event entitled "Storm Area 51: They Can't Stop All Of Us" on July 27, reportedly as a joke.

But within a week, more than two million Facebook users had RSVP'd, with another 1.2 million marking themselves as 'interested' in attending.

In the ensuing weeks, hype around the secret US military base in the Nevada desert reached fever pitch, with hundreds of articles and social media posts detailing the site's mysterious history and exploring the rumours evidence of extraterrestrials was hidden there.

The US Air Force responded sternly to the event, warning the public not to trespass in the area or face 'lethal force' and arrests.

Facebook later shut the event page down, but social media crusaders vowed the 'storming' was still on, encouraging those interested in discovering the truth make the pilgrimage on the previously agreed date.

When push came to shove, however, enthusiasm fizzled out, leaving the world none the wiser to whatever actually goes on in the base the US Air Force insists it uses solely for pilot training purposes.