A large waterspout formed in front of stunned tourists in Thailand.

Footage shows the funnel-shaped weather phenomenon gaining size off the coast of Pattaya, Chon Buri province, on September 2.

The thick vortex was connected to a low-lying clump of storm clouds above and lasted up to 15 minutes.

Boats offering tours were warned not to sail and return to shore, while jet ski rentals had to cut their business hours short.

Onlooker Kanyanat Boonying said: 'The sky was dark, and it looked like it would rain this morning. Some were preparing to enjoy the beach despite the bad weather, then the waterspout appeared.'

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.