People living near the once-secret military research base of Area 51 are bracing themselves for a huge influx of people in the coming days.
Earlier this year, more than two million people signed up to an internet joke promising to storm Area 51 in a whacky bid to "see them aliens" on September 20.
While at first dimissed as a bit of fun, the Facebook event caused such a huge storm that US Air Force officials were forced to issue a stark warning to keep people away from the base.
“The US Air Force always stands ready to protect America and its assets," AirForce spokesperson Laura McAndrews said.
Though the creator of the Facebook event, Matty Roberts, later called it a hoax, the overwhelming response sent local, state and military officials scrambling. It became so big that locals planned festivals such as Area 51 Basecamp, Alienstock and Area 51 Celebration in its honour.
Facebook user Jackson Barnes, who was responsible for designing an elaborate “game plan” for the occasion, wrote on the event page: “Hello US government, this is a joke, and I do not actually intend to go ahead with this plan.
“I just thought it would be funny and get me some thumbsy uppies on the Internet. I’m not responsible if people actually decide to storm Area 51.”
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Area 51's secrecy has long fuelled fascination about extraterrestrial life, UFOs and conspiracy theories, giving rise to the events this week and prompting the military warnings not to approach the protected site.
The base tested aircraft ranging from the U-2 in the 1950s to the B-2 stealth bomber in the 1980s. The government spent decades refusing to acknowledge the site even existed, before releasing documents confirming it in 2013. Its secrecy still fuels speculation that it's where the government studies aliens.
So what is Area 51 and do people actually plan to storm it? Here’s what you need to know:
Where is Area 51?
Area 51 is located in the southern portion of Nevada, about 134km north-northwest of Las Vegas.
The site was acquired by the United States Air Force in 1955, mainly for the flight testing of the Lockheed U-2 aircraft.
What time are people storming Area 51 and will it be livestreamed?
On Facebook, organisers had planned for the raid to take place from 3am-6am PDT, which in the UK is 10am.
While one Alienstock has been cancelled, with organisers hoping everyone goes to an event in Las Vegas, locals fear that people will still turn up despite the military warning people no to.
And for those who can't make the event, a company called AREA15 has announced that it intends to film the raid.
AREA15, which calls itself an "immersive entertainment" company, tweeted: "Everyone that signed up to #StormArea51 may have called it quits. Not us! We found a small group who are still going to make a (Naruto) run for it to set the aliens free... and we're going in with them. Well, our camera guy is at least. #StayTuned."
This tweet follows on from an earlier post in whch they said they were going to live stream it.
Everyone that signed up to #StormArea51 may have called it quits. Not us!
We found a small group who are still going to make a (Naruto) run for it to set the aliens free... and we're going in with them. Well, our camera guy is at least. #StayTuned https://t.co/oRtz4kxeiv— AREA15 (@AREA15official)September 19, 2019
What is Area 51? Why has it sparked conspiracy theories?
For decades, the mysterious Area 51 has been the subject of UFO conspiracy theories, with many people believing it’s where the US government stores its secrets about extra-terrestrial activity.
Some even maintain the base is where captured UFOs and alien remains are kept, although the US government has always categorically denied this.
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In 1947, a United States Army Air Forces balloon crashed at a ranch near Roswell, New Mexico - but conspiracy theorists believe the vessel was in fact an alien spaceship and was carted off to Area 51 for examination shortly after the crash.
Others claim the government uses the site to develop weather control and time travel along with sci-fi weapons, propulsion systems and aircraft based on alien technology.
Many believe there is an railway serving facilities underground, and that there is a camouflaged runway that only appears when water is sprayed on it.
Alarmingly, some even believe that engineers hold meetings or joint undertakings with aliens at Area 51.
Arguably one of the most bizarre theories is the belief that Area 51 is used as a base for a one world government.
Why do they believe the conspiracy theories?
After years of denying it existed, in 2013 the CIA was forced to acknowledge its existence following a Freedom of Information request filed in 2013.
Its location was finally revealed and the US government admitted it was a military site, but officials never disclosed the type of activity that goes on there.
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The base's actual function remains to be a mystery and it is still constantly patrolled by armed guards, CCTV, and motion-sensor cameras.
But the secrecy surrounding the base has prompted scores of people around the world to believe the area is holding more than officials say.
Part of this is down to the sighting of apparent UFOs in the area, with many people in the past claiming to have seen alien aircraft in the skies around the base.
However, many of these supposed UFO sightings can be attributed to top-secret reconnaissance aircraft in the 1950s, specifically the Lockheed U-2 and the SR-71 Blackbird.
Not only did these aircraft have a different shape to many others at the time, but also flew at faster speeds and higher altitudes than most others too.
What was the Roswell incident in 1947?
The hugely controversial and well-known Roswell incident happened in 1947, when a man named William Brazel spotted some debris in the desert in June of that year.
One month later, the military issued a press release announcing that a "flying disc" had been found there.
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But the next day the statement was retracted with the air force instead saying it was a damaged weather balloon.
However, it wasn't until the 1990s that the true nature of crashed object was revealed - a nuclear test surveillance balloon from one of the site's top-secret projects.
The military had decided to conceal the true purpose of the crashed balloon for nearly 50 years, with the secrecy leading to many people believing the military was hiding even more than it was letting on and adding further fuel to the ongoing conspiracy theories.