Several pilot whales currently stranded off the west coast of Australia's Tasmania will be euthanised as they cannot be saved, officials said on Thursday.

Some 380 whales have already died in the country's worst stranding on record, the BBC said ina report.

Rescuers have refloated 70 of the mammals, adding that there was hope for another 20.

But they have said four surviving whales that are too exhausted to be saved will have to be killed as it is "the most humane thing to do".

"These are animals we've given a chance, we've tried to release them but they haven't done well," the BBC quoted Kris Carlyon with the Marine Conservation Project as saying.

The four whales have been assessed by a vet before the decision to kill them was taken, "based purely on animal welfare grounds", Carlyon added.

The pilot whales, whose exact population numbers are not known and were not considered endagered, washed up on sand spits around an area called Macquarie Heads.

The officials are still trying to determine how they became stranded.