Since Monday, hundreds of long-finned pilot whales have been found beached on Tasmania's west coast.
Rescuers had managed to save 50 by late on Wednesday, and they were trying to help the remaining estimated 30 whales.
Tasmanian government officials said the rescue effort would continue "as long as there are live animals".
"While they're still alive and in water, there's still hope for them - but as time goes on they do become more fatigued," said Nic Deka, regional manager for Tasmania's Parks and Wildlife Service.
He added the focus would now also shift to removing the hundreds of carcasses scattered along the coast. A clean-up plan is still being worked out - in the past carcasses have been buried on the shore or dragged out to open sea.
It is not fully understood why the whales became stranded. The species is known to be prone to getting beached.
The stranding, one of the largest ever recorded globally, eclipses a previous national record of 320 set in Western Australia in 1996.