SYDNEY - A popular beach in Sydney has been closed to the public after mysterious black balls of debris washed ashore.

Coogee Beach in eastern Sydney has been ordered closed, and an urgent investigation and clean-up operation was launched after hundreds of the ball-shaped debris were found along the length of the beach by lifeguards on Tuesday.

The local Randwick City Council said in a statement that the beach would remain closed until further notice.

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It said that it is investigating the origin of the composition of the material and that samples have been collected for testing.

"At this stage it is unknown what the material is, however, they may be 'tar balls' which are formed when oil comes in to contact with debris and water, typically the result of oil spills or seepage," the council said.

The Randwick City Mayor, Dylan Parker, told the Australian Broadcasting Corporation (ABC) that if the balls are made of oil they could be carcinogenic and strongly advised people not to touch them.

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He said he was not aware of any recent oil spills nearby.

Coogee Beach is 3.5 kilometers south of the iconic Bondi Beach and is one of the most popular beaches in Sydney. It is accessible only by stairs from a seawall, which has been barricaded to block the public from the sand.