Green 'alien eggs' have washed up on Sydney Beach - Extremely rare living algae

Thousands of green 'egg-shaped balls' have washed up on Sydney Beach and may be rare living algae.

Surfers and early morning walkers were stunned to find thousands of green 'egg-shaped balls' on Sydney beach, Dee Why; which had washed ashore overnight and may be rare living algae.

Rather than the green spheres being something from another planet, scientists explained they were a type of sponge-like seaweed that forms egg shapes possibly to protect themselves from predators.

Beach-goers said they'd never seen anything like it, describing the balls as 'alien eggs, 'alien hairballs', Japanese moss balls.

Scarlett de Villiers from nearby Davidson saw the weird balls on her regular morning beach walk.

"I picked one up and squeezed it and it was so squishy - but I wasn't sure if it was alive and was worried I might hurt anything inside!' she told the Daily Mail. 'It struck me how perfectly shaped they all were and how green and alive they looked."

About three days ago, there were a few egg-shaped balls but then today, they were much bigger and everywhere on the beach,' Naraweena resident Jenny Zhang told The Manly Daily.

Associate Professor Alistair Poore from the School of Biological, Earth and Environmental Sciences at the University of NSW said the balls were probably a rare type of living green algae, which has only been seen a handful of times around the world.

'I’ve seen similar things - sometimes dead sea grass can roll around and form balls like underwater tumbleweeds but that’s made of dead material and these look to be living,' he said.

'It is a habit known as "aegagropilious", where the algae is free living (not on rocks) and forms into spherical balls. They’re pretty interesting,' Mr Poore said.