This is the dramatic moment swimmers panicked when a monitor lizard suddenly emerged in a waterfall pool.

Tourists were swimming in the refreshing, flowing water when the large reptile, which had been clinging to a rockface, suddenly fell into the pool in Kanchanaburi, Thailand.

Footage shows the predator slipping from the boulders and plunging into the clear water at the Erawan Waterfall on July 11.

Upon seeing this, women and children wearing life vests nearby frantically swam out of the rocky basin as the animal glided across the water's surface.

Terrified holidaymakers screamed, fearing that the lizard might attack them.

The visibly unfazed cold-blooded creature calmly swam through the pool, searching for a way out.

Asian water monitor lizards normally live in canals, swamps, sewers and ponds in cities in Thailand. They feed on fish, snakes, frogs and scraps of food left by humans.

The reptiles are aggressive when threatened and have a mildly venomous bite which sometimes carries harmful bacteria. The Godzilla-like reptiles are also a protected species in the country so their population thrives.