Las Vegas: The US Air Force has warned people against participating in an internet joke that is trending on social media suggesting a large crowd of people "storm Area 51," the top-secret Cold War test site in the Nevada desert. A prank event that went viral on social media platform, Facebook attracted more than 1 million interested people suggesting that a mass of people attempt to run into the mysterious site at 3 a.m. on Sept. 20.

The site is part of the vast Nevada Test and Training Range and has become the centre of UFO conspiracy theories. The Facebook event jokes "they can't stop all of us" and "Let's see them aliens." Nellis Air Force Base said in a statement that the Air Force is aware of the Facebook posting and says "any attempt to illegally access the area is highly discouraged."