'Tar balls' washing up across famed Sydney coastline

Nearby Coogee remains closed after the dark-coloured balls were first found on Tuesday, while staff in orange Hazmat suits could be seen cleaning up the beach two days later.

Balls have also been observed in debris at Bondi, as well as Tamarama, Bronte, Malabar, Little Bay, Congwong and Frenchmans beaches, all in Sydney's east, the NSW Environmental Protection Authority said.

Randwick City Council contractors were removing the potentially hazardous material from Coogee and other nearby beaches after preliminary tests showed it was a "hydrocarbon based pollutant which is consistent with the makeup of tar balls".

Tar balls are formed when oil comes into contact with other debris and water - usually as a result of oil spills or seepage.

The source of the pollution is unknown but the EPA is investigating the incident, conducting extensive testing on a number of samples.

"At this stage, the origin and contents of the balls remains a mystery," the agency said, adding it had not yet confirmed the presence of hydrocarbon as suggested by council tests.

Preliminary tests indicate black spheres found at Coogee Beach were balls linked to oil. (Dan Himbrechts/AAP PHOTOS)

"Until the clean-up is concluded, we advise against swimming and touching any balls that may have washed ashore," the EPA said.

Randwick mayor Dylan Parker said community safety was the top priority and the beaches were closed as a precaution while the material was collected and disposed of.

"We don't yet know what has happened to produce the debris washing up on our beaches, but we will continue to work with relevant authorities to ensure the safety of the public and clean up our beaches," he said.

Members of the public have been urged to avoid touching the material.

Premier Chris Minns said authorities needed to ensure people were safe and as soon as environmental officials knew the source of the pollution that information would be shared with the public.