Where is Area 51 on Google Maps? And what is the Storm Area 51 Facebook event?

More than one million people have joined a Facebook event pledging to raid Area 51 – a restricted area of Nevada in the US where conspiracy theorists believe alien activity to be taking place.

Organisers of the event called “Storm Area 51, They Can’t Stop All of Us,” are determined to invade the highly classified site on Friday September 20, between 3am and 6am.

"We can move faster than their bullets," the event page promises those who RSVP.

Despite being a satirical event, officials have issued stark warnings to potential trespassers.

Air Force spokesperson Laura McAndrews said: "[Area 51] is an open training range for the US Air Force, and we would discorage anyone from trying to come into the area where we train American armed forces."

She added: "The US Air Force always stands ready to protect America and its assets."

So what is Area 51 and why are people planning on storming it? Here's what you need to know:

What is Area 51?

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.

In 1947, a United States Army Air Forces balloon crashed at a ranch near Roswell, New Mexico.

Conspiracy theorists believed that the vessel was in fact an alien spaceship, and was carted off to Area 51 for examination.

Others think the US government uses the site to develop sci-fi weapons, weather control and even time travel.

In 2013, the area was officially acknowledged as a military site, but the government has never disclosed what type of activity goes on there.

On Saturday 20, organisers of the event are planning to conduct a “Naruto run,” as they approach the site, a term which refers to a Japanese anime style of running with the arms thrust backward and the head stretched forward.

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.