The startling account is being examined by the US-based Mutual UFO Network (MUFON) the world’s biggest organisation dedicated to UFO and alien research.
The unnamed witness, from Mesquite, Nevada, has filed a report to MUFON, in which he suggests that the cylinder-shaped UFO may have disappeared into a wormhole – which is a theoretical portal to another dimension.
He said it happened after there was fighter jet activity near the Nellis Air Force base in Las Vegas, Nevada.
According to alien conspiracy theorists the base is where the US military secretly carries out tests on UFO technology recovered from visiting aliens.
One, Scott C Waring, of ufosightingsdaily.com, even claimed that a known species of aliens called the “Tall Whites” are actually based inside Nellis Air Force Base where they help the USAF develop their technologies in exchange for mineral resources they require on their planet.
There is no known evidence to support this theory other than it being repeated on various conspiracy theory websites.
The alleged witness was inside watching television at 8.17pm local time on March 19, while his daughter played outside with friends, when things allegedly got strange.
He wrote: “I heard a loud roar outside, I went out my second-floor sliding door onto the porch. There were a lot of kids playing below when suddenly a fighter jet flew lover over my apartment building.
“I could see the afterburners burning a flame it was so close.”
He said he watched for 45 minutes and there were two fighter jets involved.
It was so loud people came outside from 50 apartments, he said.
The man said one jet flew off towards the air base, the both were gone.
He added: “The other fighter reappeared maybe ten minutes later coming over the mountain, diving over the city again, low, then up and out of sight.
“I thought it was over then I heard my neighbour in the next unit over yell ‘what’s that?’.”
He said he looked up and just above the three-storey block opposite him about 100 feet in the sky was “a long tube.”
He added: “A bright yellow, maybe 60 feet long, tube coming towards me.
“It was round like a snake and big enough to drive a three-storey house through.
“As it came towards me, it made a sharp U-turn, like a plumbing pipe, then slowly dissipated.
“My guess, a large worm hole opened in the sky, then closed.
“It was now dark, the jet was gone.”
MUFON is investigating the case to see if other witnesses will speak.
But, readers of the initial report are sceptical.
One poster, calling himself Doctor Moebius posted on the MUFON website: “‘Witness speculates UFO moved through worm hole’… wow. Now THAT’S science. Not.
“I speculate the vehicle moves so fast that the witness cannot discern acceleration; I speculate the vehicle’s artificial gravity drive creates an Alcubierre-Puthoff bubble which provides invisibility for the disk, as light bends around the active bubble.
“I could speculate more, but then, that wouldn’t be very scientific now, would it?”