A fish has been pictured swimming inside a jellyfish off Australia's east coast in a remarkable and rare image that has gone viral, with more than two million online views.

Underwater photographer Tim Samuel was in the water with a friend near popular tourist resort Byron Bay in December when they came across the little creature trapped inside the only slightly larger jellyfish.

The expression on the golden fish's face -- visible through the transparent jellyfish -- appears to be one of fear.

"He was trapped in there but controlled where the Jellyfish was moving," Samuel wrote in a post on Instagram.

After the image was reposted by @discoverocean on Monday, Samuel said his phone started "going crazy".

"When @franny.plumridge and I stumbled upon it we knew we had found something special, but no idea just how unique and rare this sighting was," he wrote.

"I'm completely blown away by all the attention it is getting from all over the world."

Some speculated that the fish was being stung, while others pointed out that part of its tail appeared to be still outside the jellyfish, providing a clue to its apparent ability to steer.

Marine life expert William Gladstone confirmed the rareness of the shot which has been viewed more than 2.3 million times on imgur.

The academic from the University of Technology in Sydney told The Sydney Morning Herald he had seen a young trevally -- a species of fish -- hide among jellyfish, but had "never seen one like this where the fish is just a little smaller than the jellyfish". 

Samuel said he had considered whether to "set the little guy free", but ultimately decided it was best to "just let nature run its course".

SourcE: AFP