Mysterious black globules have washed up on a second Sydney beach, as authorities say they have identified the strange debris as oil-linked “tar balls”.

Thousands of balls were found peppering Coogee Beach on Tuesday, forcing its closure.

They have also since been found on the nearby Gordons Bay Beach.

Randwick City Council said preliminary tests indicated the stuff 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.

Both Coogee Beach and Gordons Bay Beach remain closed amid a clean-up to remove and dispose of the thousands of spheres the size of golf balls.

Tests are also being done to determine whether there is any danger to humans.

Access has been barred to Coogee Beach while the mysterious debris is tested.

“Our community is rightfully very protective of our natural environment and this has been a very concerning incident,” Randwick mayor Dylan Parker said.

“Our priority as a local council is to keep people safe and protect as far as possible our coastal and marine environment.”

Parker said a specialist waste removal contractor was systematically removing the debris from the beaches. The process would likely continue on Thursday.

Local authorities remain unsure about the scale or origin of the pollution incident, he said.

Parker said he wasn’t aware of recent oil spills nearby.

“If it is made of oil, it can be carcinogenic,” he told ABC TV.

“We’re strongly advising people just not to touch them.”