A large waterspout tornado shocked fishermen as it swirled off the coast of Indonesia.

Footage shows the cyclone's funnel extending from a mass of dark clouds down to the waters near Tarakan City in North Kalimantan Province on June 13.

Onlooker Achmad Maddar said: 'Initially, the clouds were so dark and thick, then suddenly, a large vortex appeared. It spun around for quite a while before it finally disappeared.'

The tornado reportedly lasted for about 30 minutes before dissipating.

Nofrida Handayani from the Tarakan Meteorology, Climatology and Geophysics Agency said: 'This phenomenon occurs because of cumulonimbus clouds. Then there is a process of downdraft and updraft convective circulation that causes strong winds.'

Waterspout tornadoes are intense columns of swirling tornado clouds that form over a body of water.

They are most commonly found in subtropical areas and disappear shortly after they come into contact with land.

Scientists believe they are formed when pockets of warm air near the water surface rise suddenly.

Cooler air is then sucked into the low-pressure air, which picks up water and rises towards the clouds in a rotating motion.

They very rarely damage buildings as they dissipate when they reach land. However, they are dangerous of boats caught in their path or aircraft that fly through them.