The city has warned that Coogee Beach “will remain closed until emergency services can locate and collect all black balls that have washed ashore.”
Officials also said this had never happened before.
“We are taking steps to safely collect and remove the discovered objects from the beach and are inspecting the surrounding area,” they added.
Some of the balls were sent to the Environmental Protection Agency for examination.
An unusual metal cylinder was found off the coast of Australia last July. He lay on the sand near the town of Jurien Bay. The area was cordoned off, then the strange object was wrapped in plastic and removed.
