Sydney — Hundreds of mysterious black tar-like balls have washed up on two popular Sydney area beaches, prompting lifeguards to close the strands to swimmers.

“Mysterious, black, ball-shaped debris” began appearing on Coogee Beach in the Randwick area on Tuesday afternoon, the local mayor said, leaving flummoxed Australian authorities scrambling to find out what they might be and where they came from.

Hundreds of golf-to-baseball-sized spheres could be seen littering the coast, which is usually thronged with Sydneysiders and tourists.

Instead, a few seagulls wandered among the spheres, pecking and examining.

The balls were also spotted at nearby Gordon’s Bay, an aquatic reserve popular for snorkeling and fishing, which was also closed.

“At this stage, it is unknown what the material is,” Mayor Dylan Parker of Randwick city said in a social media post. “However, they may be ‘tar balls’ which are formed when oil comes in to contact with debris and water, typically the result of oil spills or seepage.”

The balls on Sydney’s picturesque shores aren’t the only unidentified objects to appear on beaches lately. Officials in Canada confirmed to CBS News on Tuesday that they were investigating blobs of a white “mystery substance” that have washed up since September on beaches in the far northeast Newfoundland and Labrador province.

Canada’s environmental agency told CBS News’ Ahmad Mukhtar that samples of the hundreds of white blobs littering beaches had been taken, but that both the substance and its origins remained a mystery.