A giant human-sized jellyfish has stunned a diver off the south-western coast of England.

The creature, commonly known as barrel jellyfish, was spotted near Falmouth by Lizzie Daly, a broadcaster at BBC Earth and a wildlife biologist with Wild Ocean Week.

Daly described this encounter as "breathtaking."

She said:

"What an unforgettable experience. I know barrel jellyfish get really big in size, but I have never seen anything like it before!"

In a video meeting, she added:

"It was the best thing I've ever done."

Daly swam next to the giant jellyfish that appeared to be as big as her body. A video of this jellyfish has gone viral and was taken by Daly's underwater cinematographer, Dan Abbott.

The cream-colored barrel jellyfish was spotted off the coast of Cornwall, England, and its size and location have shocked many.

Daly said the creature isn't all that unusual nor harmful.

Daly told CBS News:

"It's known to get this large, but I haven't seen one this big. Dan said he hasn't seen one this big either."

"Their appearance is quite distinctive... They're the largest jellyfish you can get here in the UK waters."

"They're not a threat to humans. They have a mild sting, but wouldn't cause damage to humans."

Daly and Dan Abbott were on a seven-day marine adventure to promote the conservation of all the marine wildlife species around the UK.

She explored the waters as part of her campaign, the "Wild Ocean Week."

According to Wild Trusts, barrel jellyfish can grow up to 3.2 feet and weigh up to 25 kilograms (55lbs). They're also called dustbin-lid jellyfish because they can grow as large as dustbin lids.

They have a translucent appearance, a massive mushroom-shaped bell, and a bunch of eight frilly tentacles on the underside.

Their frills contain small stinging tentacles that surround hundreds of little mouths.

In the UK, they're frequently found washed up on the coastlines during summer.