Twin waterspouts that erupted over the Hooghly river near Sagar Island on Friday morning sent waves of panic at Mahishamari in South 24-Parganas, forcing fishermen to abandon their nets and race back to shore.

Two towering columns of swirling water rose dramatically towards the sky — the spectacular yet frightening phenomenon, believed to have been triggered by severe atmospheric instability over the estuarine region where the Hooghly meets the Bay of Bengal — was witnessed around 11.30am.

Residents, fishermen and boat operators watched in astonishment as two tornado-like waterspouts developed almost simultaneously over the river.

As the giant columns of rotating water gathered strength, fear quickly spread among people navigating the river. Small fishing boats and trawlers hurriedly changed course and returned to nearby ghats, anticipating the onset of violent weather.

Resident Manas Biswas said: "At first, the water began to swirl in the middle of the river. Within a few minutes, the rotation intensified, transforming into a waterspout. Surprisingly, another swirling waterspout formed a short distance away from the first one."

"Witnessing such a scene was a once-in-a-lifetime experience. But at the same time, it created panic as the weather changed rapidly with strong gusty winds," Biswas added.

He went on: "Many villagers who were on the river bank, began recording videos on their cellphones, while others ran in fear seeking safe shelter."

Local fishermen said they had rarely encountered such an extraordinary phenomenon over the Hooghly. One fisherman, who was aboard a fishing boat when the waterspouts formed, said: "The river water suddenly began to swell abnormally, and wind speeds surged in an instant. Realising the gravity of the situation, small boats and fishing trawlers on the river were quickly moved to safety. Many trawlers even turned back from mid-river towards the ghats."

The twin waterspouts persisted for only a few minutes before dissipating. However, the weather changed dramatically immediately afterwards. Thick black clouds engulfed the sky, powerful gusts swept across the island, and heavy rain lashed large parts of Sagar Island within a short span.

Climate experts attributed the rare phenomenon to a combination of high atmospheric moisture, intense surface heating, sharp temperature contrasts and localised changes in air pressure.

Explaining the possible cause behind the waterspouts, Tejashi Roy, assistant professor in the department of geography at Krishnanagar Government College, told The Telegraph: "Over the past few days, south Bengal has experienced intense heatwave conditions, creating high temperatures and abundant atmospheric moisture. These factors led to localised low-pressure systems and an unusual cyclonic event that produced twin waterspouts resembling tornadoes."

Further explaining the phenomenon, Roy's colleague in the geography department and climate science expert, Mehedi Hasan Mandal, said: "Such phenomena develop when strong atmospheric instability, moisture and wind shear interact. Warm, humid air from the Bay of Bengal rises rapidly to form towering cumulonimbus clouds."

"Powerful updrafts and rotating winds can generate twin funnel-shaped vortices within the same storm system, resulting in rare twin waterspouts," Mondal added.

The local administration has urged people living along the riverbanks to remain alert. Boat operators, trawler crews and fishermen have been advised to monitor weather forecasts carefully and avoid venturing into the river during periods of unstable weather.