The US state of South Dakota witnessed an extremely unusual phenomenon after its sky turned an ominous, bright green in appearance on Tuesday.

According to experts, the phenomenon was caused by a wind storm called "derecho," which is associated with rapidly moving showers or thunderstorms.

The powerful storm extended more than 240 miles and passed through South Dakota and other parts of the plains, according to the US National Weather Service (NWS).

The NWS defines this wind storm as a long-lived, widespread, straight-lines storm that generally has no twists and turns like tornadoes or hurricanes. Unlike other tropical storms, these are rare. The change in the colours could be attributed to the way atmospheric particles interact with and scatter sunlight.

"It takes a tremendous amount of water content within the cloud to achieve this colour, which usually means a substantial amount of ice (large hail) has to be present!," explained NWS meteorologist Dr. Cory Martin, per Times Now.

The unusual sight left the residents of South Dakota, storm chasers and netizens surprised and several of them took to social media to share the images of the eerie green sky.

"Green Sky's all of a sudden in South Dakota USA," wrote a Twitter user along with several images. "Going green this evening as a powerful derecho sweeps through Sioux Falls South Dakota with damaging winds and hail pic taken by Jaden," wrote another.

In one of the videos that made it to social media, a person could be heard comparing the dramatic scenes to those witnessed in the popular series Stranger Things.

According to Peter Rogers, a meteorologist with the Weather Service's office in Sioux Falls, it is not unusual for the sky to turn completely dark, purple or red before or during a storm. But the sky turning green is a rare occurrence.

"I think it caught a lot of people's attention because the sky did have that very unique green colour to it. Because of the unique colour that it did exhibit, I'm guessing that it will probably be a topic of discussion for quite a long time," Rogers told The New York Times.

Wind and rain from Tropical Storm Andrea hit the Florida coast near Gulfport, Florida on Thursday. Reuters / Steve Nesius Reuters/Steve Nesius