Stunned witnesses in Novosibirsk city, Russia, are heard calling out to each other at the sight of the eerie ring which remained in the sky before disappearing into clouds.
It was filmed above the Siberian Mall shopping centre and footage of the event has gone viral online after it was uploaded to social media.
One viewer wrote: “This looks like some kind of creepy warning.”
Another commented: “It’s a kind of supernatural power flying across the city!”
And a third replied: “Aliens are coming to get us! Scary!”
An actual witness speculated that it was a weather event.
They said: “The smoke ring is nothing but a soliton.
“Black hydrocarbon with the vortex making up a ring and lifting it into the air.”
But a weather expert, who remained stumped about what the black ring was, did not agree.
Renad Yagudin of the Siberian Hydrometeorological Centre said: “There is no such definition in meteorology as a soliton.
“This is not a meteorological event.”
However, UFO hoax buster Scott Brando, who runs website ufoofinterest.org appears to have cracked the case.
There have been a number of similar rings reported across the globe in recent years, including one over Disneyland, California, in June.
He said they are caused by a giant smoke ring firework which leaves the black ring hanging in the air after being set off.
He pointed to footage he used to expose the hoax last June which shows the ring being created after one is set off.