The flashing white and red lights were seen travelling in a line formation as they travelled west across the US towards Nevada.
Residents from Columbia, South Carolina, to Missouri, Illinois and Denver, Colorado reported seeing the lights pass overhead and was even picked up by national news channel CBS and Denver station 9News.
Some witnesses described the line of lights in the sky as “creepy”, saying they were silent as they passed over between 8pm and 9pm local time on Saturday.
One witness filming the event said: “A bunch of weird lights over Denver. There was like an asteroid… it was almost like a fireball that came down and now, all of a sudden, they look like a bunch of helicopters.
“There is some crazy stuff going on right now.”
That’s a cover up. You can see the lights are obviously even and connected to something.
Their footage was uploaded onto UFO YouTube channel Thirdphaseofmoon released a video entitled ‘What Just Happened Over Denver, Colorado? Major UFO Event!’ which questioned explanations saying it was an unannounced US Air Force (USAF) exercise.
The large aircraft reportedly flew to Nevada for a training exercise involving HALO drop high-altitude military parachuting.
Aviation expert Steve Cowell said the planes were flying in a formation that is commonly seen in military exercises.
He said: “That was the echelon formation. In other words, they were all lined up in a row. “It is not uncommon to have these types of planes in formation, especially at night. Often times, you will see them doing this, especially when they are doing training flights, or standard cross country procedure.
“Don’t assume it is a UFO. Not until the bulletin comes over the news.
NOT ALIENS: However, conspiracy theorists have not accepted the official explanation.
“(C-17s) have been modified to be just a little quieter. They are also flying a little slower. At that kind of power, you are not going to hear a lot of noise.”
News station 9News later reported: “We can now tell you that Saturday’s light show was courtesy of a group of 17 C-17 cargo jets. “According to our sister station WLTX, they took off from Joint Base Charleston base around 7pm EST Saturday.”
But conspiracy channel Thirdphaseofmoon was unconvinced, thinking aliens could be behind it.
The video narrator said: “This is interesting because, you clearly heard the witness say he saw some sort of asteroid or fireball break up over Denver.
“Is this some kind cover up? What were they investigating? Is this some kind of coincidence?”
The channel also speculated it may have been one huge “mile long” craft as opposed to individual military aircraft.
Subscribers to the channel were convinced of a cover up.
Seth Donahue posted on YouTube: “That’s definitely one whole UFO.
“Huge. You can see its saucer shape. No way it was planes in formation. Nice try government.”
Shelly Baham added: “That’s a cover up. You can see the lights are obviously even and connected to something.
“Either an extremely large “cigar shaped craft” or a saucer.
“Either way, that is not of this world. I wish the US would just tell the truth.”