The young Cuvier's beaked whale, or Ziphius cavirostris, was spotted in shallow waters in the area of Vouliagmeni on Thursday before divers were called to guide it back out to sea.

But it reappeared in a seaside area near Athens on Friday morning.

The species typically lives in much deeper waters, leaving experts fearing the worst for the young whale.

"The fact that it has appeared in shallow waters means it isn't at all in good health," environment and deputy energy minister Giorgos Amyras said at the scene.

"At this moment the animal is suffering."

Vets have taken a blood sample to help diagnose the injured whale and have given it an antibiotic, he added.

Two specialised vets, a specialised veterinary nurse and four aid organisations have also been brought in to try to save it.

"The prognosis unfortunately isn't good," Mr Amyras said.

"But we, of course, are doing everything possible to save the animal, which is a Mediterranean species, a jewel of the Greek seas, and I hope it makes it and that we can help it."