One of Sydney’s most popular beaches remains closed as authorities try to work out whether there is any danger from the mystery “tar balls” that have washed up.

An extensive effort was under way at Coogee Beach, in Sydney’s east, on Wednesday after lifeguards found the mysterious ball-shaped pieces of debris littering the sands on Tuesday afternoon.

Hosts of council workers could be seen gathering the balls into piles above the high-tide line and then onto trucks.

Randwick City Council has sent some of the mystery objects for testing, suspecting they might be “tar balls”, which form when oil comes into contact with debris and water.

Such events are typically due to oil spills or seepage. They can also occur naturally from seeping crude oil – and are common on Californian beaches from seepage on the ocean floor.

Local mayor Dylan 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.”

The Sydney Morning Herald reports that lifeguards on jet-skis found what they believed to be a small, dispersed oil slick off the beach on Wednesday morning. A Port Authority vessel was sent to investigate.

Test results from the suspected “tar balls” are expected later on Wednesday.

 

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However, authorities are also wary that a high tide due about 2pm could bring a further influx – so the beach remained shut.

“Beaches close from time to time for a range of different reasons –water pollution, large storm events and the like,” Parker said.

“We have taken a precaution to close the beach and hopefully we will have it open soon. Until that work happens, best to go for a walk, go to the park or visit another part of Sydney.”

Locals deprived of a swim on Wednesday were disappointed but philosophical.

“We saw the news last night and everyone messaged me last night because everyone knows I like to come down to the beach first thing in the morning, six o’clock, without fail,” one woman told ABC TV.

“If they don’t know what contaminants are in there and when it is safe to go in again it is a precaution well needed.”

NSW Environment Minister Penny Sharpe said Coogee was the only Sydney beach where the balls had washed up.

“It’s an unusual occurrence … the other beaches are fine, but we hope to get to the bottom of what is a pretty unusual situation as quickly as possible,” she said.

The NSW Environment Protection Authority is working with Randwick City Council to determine the cause of the wash-up.

-with AAP