The strange event was caught by a camera of www.webcamsdemexico.com, which has a series of livestreams continuously monitoring magma mountains across the central American country.
The footage was taken at around 6.46pm local time on January 24, according to YouTube channel Streetcap 1, which broadcast it in a video entitled “Awesome Weird Light leaves Mexican Volcano”.
Alien chasers think it could be evidence of an secret base inside the Popocatépetl Volcano in the Puebla region of Mexico.
Others think it could be a secret military base and the UFO was actually an alleged top-secret triangular spy plane known as a TR-3B which can allegedly hit “warp speed” in a ball of light.
A still from the video and (inset) a CGI image of an alleged TR-3B.
The footage shows a small bright light appear from behind the volcano in the background of the shot, which then moves closer to the camera.
The image suddenly increases in size and intensity of light before going out of shot.
Some alien chasers claim there is much UFO activity around volcanoes, because there are secret alien bases inside.
There appears to be no actual evidence for this madcap theory, and sceptics say the UFOs are just magma, or ash being ejected from the volcano, or even out of focus birds.
But the latest ball of light in this video has set tongues wagging, with claims it was a TR-3B.
Conspiracy theorists, who also believe world leaders capture flying saucers and reverse engineer them before creating their own hi-tech space craft, claim a mysterious US Air Force TR-3B has been developed.
The TR-3B, pictured here in a CGI impression, is a legend among UFO seekers.
The TR-3B is alleged to be a secret “black project” spy craft of the US Government that can be flown into space.
Allegations include the crafts are created at top-secret military bases like Area 51 in Nevada, by reverse engineering alien technology.
Others claim they are actual UFOs flown by aliens.
The theory claims they are triangular in shape with lights at the corners and a large circular one in the middle that can blast it into warp speed.
Scott C Waring, editor of UFO Sightings Daily, said: “This UFO was caught by Streetcap1 over Mexico coming from a volcano. It starts out far away and quickly grows in size.
“That’s one powerfully bright UFO. As you can see from looking at the time, the UFO passes the volcano and then moves behind the camera all in just a few minutes. The moon could not do that.”
That’s one powerfully bright UFO. As you can see from looking at the time, the UFO passes the volcano and then moves behind the camera all in just a few minutes.
Viewers of the video were amazed, with many posting on YouTube: “OMG and WTF.”
One posted: “WTF is that?!! OMG, I’m so scared it’s huge!!!”
Another said: “TR3B 100 per cent. I have done a lot of research, which is freely available.
“I was fortunate to see a similar light above my house, I was gobsmacked, all my research made sense
“It’s a plasma ball of light in the craft’s middle, you will normally see this on black triangle crafts.
“The plasma light extends to cover all the craft and then will normally disappear cloaking the craft.
“These are facts – God knows how long this technology has been available.”
Another commented on the speed, saying: “The video is being played at one frame per second, meaning whatever that thing is it’s going at very high speeds.”
1 of 10
And, Leandro Murta added: “Just wonder how fast it is from volcano to camera in about 50 seconds, very interesting.”
Another poster went back to the alien theory, suggesting: “What if extraterrestrials live in volcanoes because they’ve got tech that can withstand tremendous heat? It would make a good hiding place, you know.”
Scott Brando is a sceptical UFO investigator who claims there has never been any inexplicable UFO video or picture taken yet.
He runs the hoax-busting website ufoofinterest.org.
The expert was not phased by the seemingly extraordinary footage and concluded that the bright light effect was caused by the camera having a long exposure, because it was filming at night.
He said it was likely just a standard plane or helicopter.
He told express.co.uk: “Webcams are often set to take images at night with a long exposure, to capture every small source of light. That object is most likely a plane (or a helicopter) with its navigation/landing lights.”