Black, ball-shaped debris washes ashore on Sydney's Coogee ...

Hundreds of mysterious black spheres have washed up on Coogee Beach, raising safety concerns and leading to the closure of the popular eastern Sydney beach.

Randwick City Council announced the beach would be closed until further notice while the suspected "tar balls" are cleared and their origin is investigated.

Mayor Dylan Parker told ABC News Breakfast that the council was not sure what is washing up on Coogee Beach.

"This is the first time that an incident such as this that we're aware of has happened in the Randwick council area," he said.

Cr Parker said environmental authorities had been notified and teams worked through the night to clear the debris.

The debris washed up on Coogee Beach on Tuesday. (Supplied: Randwick City Council)

He said the debris "may be tar balls".

He said they are "dark ball-shaped objects which occur when they're in rough seas and when oil comes into contact with debris or water and is typically the result of oil spills or seepage".

"If it is made of oil it can be carcinogenic. We're strongly advising people just not to touch them."

The mayor said he isn't aware of recent oil spills nearby.

The council is assessing other beaches in the area but claims the incident appears to be isolated.

Environmental officers collected samples of the contaminant for testing. 

Randiwck City Council is investigating the origins of the debris. (Supplied: Randwick City Council)

Local residents Tina Stamell and Dan Forgette, who swim at the beach every morning, were disappointed by the closure.

"It's a bit frustrating, but I understand," Ms Stamell said.

Sydney's Coogee Beach has been closed following the discovery of black, ball-shaped debris on  October 16, 2024. (Supplied: Randwick City Council)

Ms Stamell has been swimming at the beach for about 40 years and said she had never seen anything like the black spheres before.

"We've seen a lot of debris from all [of] the storms," she said.

"But this is something unusual, very unusual."

Tina Stamell and Dan Forgette swim at the beach every morning. (ABC News: Myles Houlbrook-Walk)

Mr Forgette said the pair came down to the beach this morning to see if the debris "had cleared up".

"I guess they [Randwick City Council] don't know what contaminants are in there and when it's safe to go in again," he said.

"I guess it's a precaution well-needed."

Council workers continued clearing the beach of the debris this morning. Some were seen wearing face masks.

The council is asking people to avoid Coogee Beach until further notice.

The mayor said the beach would reopen when the authorities say it is safe to do so.