At least 80 whales and dolphins have died after beaching themselves on a remote island between the Australian mainland and the country's island state of Tasmania.

The number of deaths on King Island could be higher as some bodies might have been washed back out to sea, said Warwick Brennan, a spokesman for Tasmania's Department of Primary Industry, Water and Environment.

"What we found at first light this morning...was 80 animals strewn along several hundred meters of beach. All those animals were dead," Brennan said on Monday.

"There was a mixture of adults and juvenile animals. So it was a very grim sight," Brennan told Australian radio.

He said there were 55 dead long-finned pilot whales and 25 dead bottle-nosed dolphins on King Island beach, around 250 km (160 miles) south of the Victorian state capital Melbourne. A further 17 whales were swimming around 1 km offshore.

"The immediate focus for the rescue team will be ensuring that the group does not come closer to shore," Brennan said in a statement. The team is made up department officers, police and volunteers.

He said it was unknown why the animals beached themselves. The deaths come a year after 100 pilot whales died on a remote beach on the southwest coast of Tasmania.