Up to 90 stranded whales died in southern Australia while another 180 are stuck, an Agence France Presse report stated.
Government marine biologist Kris Carlyon said "about a third" of the 270 animals were dead by late Monday, and that rescuing survivors would be a "challenging" task likely to take several days.
Though mass whale strandings occur relatively often in Tasmania, such a large group has not been seen in the area for more than a decade.
About 60 people — including volunteers and local fish farm workers — are involved in the rescue attempt. The animals are only accessible by boat, limiting the number of rescuers who can reach them.
Scientists said two large pods of long-finned pilot whales became stuck on sandbars in Macquarie Harbour, on Tasmania's rugged and sparsely populated west coast. The other whales followed and were got stuck in the shallow waters.
