Massive orange bulbous clouds created an eerie phenomenon in a US town this week, prompting locals to turn to social media for answers.

Residents of Iron Mountain, Michigan, posted photographs and video of the spectacle.

"All of a sudden it got very yellow outside, it felt strange and mysterious," resident Jason Asselin said. "Then it slowly looked very orange, it was the craziest thing I have ever witnessed over my head. I almost expected to see a tornado or something.

"They are extremely rare in this part of the country and many people have never seen anything like it before."

US National Weather Service meteorologist Jeff Last said the mysterious clouds were known as mammatus or "breast cloud".

Mammatus, or mammatocumulus, clouds are often associated with severe thunderstorms, according to the Iron Mountain Daily News.

"The pictures don't really capture how eerie the whole experience was," reporter Chris Tomassucci said. "The mammatocumulus that formed over Iron Mountain made everything take on strange coloration. Greens looked more green, blues more blue, and so on."

The front crossed the Upper Mississippi River Valley region during the afternoon and evening. A southerly flow ahead of the front brought a warm and muggy air mass, which provided fuel for severe thunderstorms that fired on the cold front. Numerous reports of severe weather were received, mostly in the form of hail and a tornado.

The weird cloud formation. Credit: Joe Nottage/Facebook