The footage, uploaded to YouTube by the channel Section 51 2, shows a distant shot of a giant hovering rhombus-shaped UFO with a separate bright orb moving around it.
It is seen to rise into clouds above as if disappearing through a portal to another dimension.
The Section 51 2 website claims it was filmed in November 2016 by Danish fishermen.
However, it includes no real details about the alleged sighting.
An article accompanying the video on the Section 51 2 website makes no further reference to the alleged sighting in the video.
It instead discusses a 2011 sighting over the North Sea.
It is likely the video is a clever hoax made using CGI technology.
One viewer posted on YouTube: “You guys are doing a great job with the CGI, I hope one day you guys could make a vid of ufos fighting and stuff.”
But, amazingly, some thought it could be genuine footage with claims it looked like a legendary mythical UFO called the Black Knight Satellite.
Margaret Bu Shey posted: “Everyone handles their fear or unexpected events differently.
“To discount a video because someone isn’t screaming limits one’s possibilities of finding out the truth/facts of the matter.”
And, Robert Kimball said: “The large shape is a sampling collector that will be beamed into a large mother ship cloaked in the dark cloud.
“The little light orb is a small sensor ship making sure it is safe to beam up the sample.
“We have benevolent ET friends who are serious about helping clean up our mess – starting with the ocean. be happy.”
But, Section 51 2 has been outed by serious UFO investigators and hoax busters as regularly using GCI effects to add extraordinarily clear-looking UFOs to its videos.
The website and channel features on many UFO investigators “blacklists” of so-called UFO sites to avoid because of its alleged use of hoaxes, which “discredit genuine research”.
The ‘about section’ on its website suggests it broadcasts genuine footage, saying: “Sometimes we have no words to explain what we see, sometimes we can see that it’s just hoax.
“The purpose of Section 51 is to make you ask yourself these questions about UFOs… Many UFO reports from soldiers exist all around the world but some people want to hide the truth.
“Section 51 shows you UFO incidents reported by people and most of the time by soldiers in wartime.”
But there is a disclaimer on its YouTube page, which suggests otherwise.
It states: “These videos are for entertainment purposes only.
“We cannot authenticate all videos. Viewers are free to make their own conclusions.”
Scott Brando, who runs hoax-busting website ufoofintererst.org, said the channel “clearly” broadcast out and out hoaxes which had been digitally made.
Express.co.uk has contacted Section 51 2 a number of times over whether the videos are genuine but is yet to receive a response.