The discovery of the marble-sized balls comes after a similar incident in October closed Sydney's Bondi Beach, among other tourist hotspots.

Authorities in Australia say they have decided to shut nine beaches while they investigate the unusual grey and white balls.

Nine beaches in Sydney were closed on Tuesday as authorities investigated marble-sized balls of white and gray debris that had washed on shore.

Mysterious balls appear on Sydney beachesNorthern Beaches Council

Sydney’s iconic beaches are famous worldwide for their golden sand and pristine waters. They attract millions of tourists every year, but this time, they have drawn the attention of researchers and local authorities for an unusual reason.