In the remarkable footage – filmed above Toronto in Canada – four giant bright lights are seen in the night sky.
The furthest object to the left slowly moves above the skyscrapers and houses and is thought to be a helicopter.
But the three other lights remain in the same position for several minutes.
Alien enthusiasts SecureTeam10 posted the clip to their YouTube channel yesterday (June 10).
“The source of this said the things made no sound and just sat there for five minutes before disappearing,” said Tyler Glockner, who owns the site.
“They did not move or do anything.
“These three lights are just eerily hovering over the city.
“Some believe that they’re three separate entities or many believe this is one large craft.”
More than 210,000 people have seen the clip, with many users offering their own opinions.
More than 40,000 Americans have taken out insurance against being abducted by aliens.
“This has to be an alien encounter,” one wrote.
Another added: “Those three lights are not from three UFOs but one big ship!”
And a third commented: “I think it’s a cloaked mothership.”
But others were less convinced, suggesting they were simply from an aircraft.