Rescuers were headed Monday to Naracoopa Beach on Tasmania's King Island to try to save some of the 194 pilot whales and half a dozen bottlenose dolphins that began beaching themselves on Sunday evening.
Some had died by Monday morning, said Chris Arthur from Tasmania's Parks and Wildlife Service.
"While there are animals alive, there is always hope," Arthur said.
It was not clear why the animals had beached on the island, halfway between Tasmania and mainland Australia. The Examiner, a Tasmanian newspaper, reported that the animals were caught by a very low tide.
Strandings happen periodically in Tasmania as whales go by during their migration to and from Antarctic waters. However, Arthur said it was unusual for whales and dolphins to get stranded together.
In January, 45 sperm whales died after becoming stranded on a remote Tasmanian sandbar, even though rescuers worked for days to keep them cool and wet as they tried to move them back to the open water.
Last November, 150 long-finned pilot whales died after beaching on a rocky coastline in Tasmania. A week earlier, rescuers saved 11 pilot whales among a pod of 60 that had beached on the island state.
Scientists do not know why the creatures get stranded.