"Nuclear mushroom" above Kazan; Residents of Russia panic-stricken VIDEO

"Nuclear mushroom" above Kazan; Residents of Russia panic-stricken VIDEO

Residents of Kazan, the capital of the Republic of Tatarstan, said they saw a mushroom-shaped cloud in the sky on Wednesday night that resembled the shape seen after a nuclear explosion.

The local newspaper Vechernyaya Kazan later said that it was a "cumulonimbus" or "anvil" cloud. A cumulonimbus is a dense, vertical cloud that contains thunderstorms, formed by warm, moist, and unstable air that rises and rolls upward.

This causes the top of the cloud to flatten and expand into an anvil or mushroom shape. NASA says this type of cloud is more likely to form in tropical latitudes year-round and during the summer season at higher latitudes. State news agency RIA Novosti interviewed a spokesman for the Ministry of Ecology and Natural Resources of the Republic of Tatarstan who tried to allay residents' fears after the mushroom-shaped formation was spotted in the sky.

The cloud, which resembles a "nuclear mushroom", is a type of cumulonimbus, the spokesman said.

"Warm air is lighter than cold air. Its exit into the middle layers of the atmosphere can be seen in the form of a mushroom cloud. This atmospheric phenomenon is called an inversion, or an anvil cloud. This is a special type of cumulonimbus. It rises to a height of about 12 to 15 kilometers, and then it starts to fog up," said the spokesman.