An odd piece of footage from China purportedly shows a 'cloud city' that was spotted floating in the sky.

The puzzling scene reportedly left onlookers baffled and video of the 'heavenly metropolis' has created quite a stir online.

Some paranormal enthusiasts have suggested that incident was a brief glimpse into a parallel dimension or alternative world.

Meanwhile, conspiracy theorists have an even more dire hypothesis, arguing that the 'cloud city' is a test by the Chinese government of hologram technology akin to the infamous 'Project Blue Beam.'

However these fantastic scenarios are probably not the cause of the strange sight as weather experts say that the 'cloud city' is simply an optical illusion known as Fata Morgana, where perception becomes distorted due to hazy conditions and hot temperatures.

Why China seems to be the site of so many of these 'cloud cities' remains a mystery, although one wonders if it could be because of the extreme amounts of smog lingering in the air over the country's major cities.