Rescuers set free around 25 whales on Tuesday marooned on a sandbar off Australia's island of Tasmania, with hopes to refloat hundreds more within days.
But government scientists said about 90 of the 270 have died.
The pod of pilot whales were first spotted in shallow water off the rugged coastline on Monday.
Parks and wildlife regional manager, Nic Deka:
"We've rescued about 25 at the present time and escorted them out the channel and out to sea and crews are continuing to work, so that number will increase before we get to the end of the day."
The rescue has been labour intensive, physically pushing the animals or using specialized cloth and pontoons to drag them to deeper water.
Pilot whales are a species of oceanic dolphin that grow to 7 meters long and weigh up to 3 tonnes.
Around 40 scientists, 20 police officers, fish farmers and volunteers are involved in the rescue effort, the hardest experts say they have encountered yet.
Scientists do not know why whales beach themselves.
But they say when the animals travel in pods, they're known to follow a leader, and gather around a whale that is injured or in distress.