A terrifying mass of cloud left residents fearing a volcanic eruption in Indonesia.

Locals watched as a towering dark formation hovered over Bandung, West Java, on the evening of September 22.

Flashes of lightning occasionally illuminated the sky behind the cumulonimbus cloud, heightening the eerie atmosphere.

Dedy, an onlooker, said: 'We thought there was a volcanic eruption at Mount Tangkuban Perahu because there are volcanic mountains nearby. It turned out to be a cumulonimbus cloud.'

The Meteorology, Climatology, and Geophysics Agency (BMKG) issued an early weather warning for the region, effective from 5:05 p.m. to 8:00 p.m. local time.

Heavy rain, lightning, and strong winds were forecast across several cities.

Cumulonimbus clouds are tall, dense, vertical formations capable of producing extreme weather such as torrential rain, hail, powerful winds, and lightning.

They are formed by strong convection, when warm, moist air rises rapidly into the atmosphere, creating massive cloud towers that can reach tens of thousands of feet and develop broad, anvil-shaped tops.