This is the moment thousands of jellyfish invade and completely overrun the waters of an Italian port city and left nearby onlookers feeling hypnotised by the view.

The giant swarm was spotted in the deep-water port city of Trieste, located in northeastern Italy.

The ‘invaders’ are scientifically called Rhizostoma Pulmo, more commonly known as ‘barrel jellyfish’. They can be found in the Northern Atlantic Ocean, Adriatic Sea, Mediterranean Sea, Black Sea, and the Sea of Azov, and are among the largest jellyfish species in the Mediterranean.

This unusually high concentration of jellyfish individuals, otherwise known as a bloom, likely stems from human activities that disrupt the environment, as well as pollution and climate change, according to scientific theories.

Although it proves an incredibly beautiful sight, jellyfish blooms can significantly impact marine ecosystems by reducing available prey for underwater predators.

Newsflash obtained the stunning footage from TikToker Eduardo Calemme, who said he had never previously seen a place with that many jellyfish.