Marble-sized balls force Sydney beaches to close

The objects are being collected by authorities for testing

Months after mysterious black balls forced the closure of some of Sydney's most famous beaches, small marble-like debris has begun washing up on the city's shores again.

The balls - this time grey or white in colour - have prompted councils to shut nine beaches, including popular Manly and Dee Why, while authorities investigate.

Eight beaches including Bondi were closed for several days in October and a massive clean-up ordered after thousands of black deposits started appearing on the coast.

Testing by authorities determined those balls were most likely the result of a sewage spill.

Northern Beaches mayor Sue Heins said the latest balls "could be anything", according to the Guardian Australia.

"We don't know at the moment what it is and that makes it even more concerning," she said.

"There's something that's obviously leaking or dropping... floating out there and being tossed around."

In a post on Facebook on Tuesday, the Northern Beaches Council said they were alerted to the fresh debris by the New South Wales Environmental Protection Agency (EPA).

The agency and the council planned to collect the discoveries for testing and inspect other beaches in the area too.

Anyone who spotted the balls was urged to contact authorities, the council added.

Though widely reported to be "tar balls", the debris in October was later found to contain everything from cooking oil and soap scum molecules, to blood pressure medication, pesticides, hair, methamphetamine and veterinary drugs.

Scientists said they resembled fat, oil, and grease blobs - often called fatbergs - which are commonly formed in sewerage systems.

However Sydney Water reported there were no known issues with waste systems in the city, and authorities still don't know the source of the material, prompting some to express concerns about the safety of the city's beaches.

"The EPA can't explain the source of the human waste causing the fatbergs and it can't assure the public that Sydney's beaches are safe to use," state politician Sue Higginson, from the Greens party, said in a statement in December.