Haikou City, China - Videos of a spectacular and rare rainbow pileus cloud astonished internet users, showing the natural wonder as it reportedly appeared in China at sunset. Yet, debate has raged over whether the images are real or fake.

Some residents in China allegedly managed to capture a fantastic climate spectacle on the evening of August 21.

Videos and images of the large cloud soon went viral on Twitter, with many viewed and re-tweeted millions of times.

In videos of the phenomenon, the colors of the clouds are extremely bright and picturesque, looking like heaven on earth.

But users beware, as the videos have been accused of being heavily edited and distorted.

As meteorologist Scott Duncan pointed out, while the event did happen, the lighting conditions in the videos are "over-saturated" and "the surrounding clouds do not make sense meteorologically."

Yet, the weather gem is indeed a real occurrence. So what's behind the mysterious iridescent cloud?

The natural spectacle known among experts as a pileus cloud, or a "cap" or "scarf" cloud, usually forms in the evening and then creates a "shimmer" of cloud cover.

According to reports, fast rising hot air from a cumulus cloud pushes against the colder air above it, creating a gentle "scarf" effect as moisture condenses at the top of the updraft.

The ice crystals and droplets in the "scarf part" of the cloud then refract sunlight hit at just the right angle, creating the cloud's incredible rainbow effect. The clouds must be very thin and made up of ice crystals or water droplets of uniform size.

Pileus clouds are usually short-lived and are soon absorbed by the growing cloud below through the process of convection.

They can be a sign of severe impending weather, and can also form over mountains, during volcanic eruptions, and other types of ash clouds.

It is unclear whether the sight could be a bad sign for China, which is currently experiencing its worst heatwave, drought, and lowest river levels in decades.

The country has tried to combat its droughts by firing rockets and drones into the sky to seed clouds with a chemical to make artificial rain.