Rescuers said Wednesday that 380 pilot whales that became stranded in a remote southern Australian harbour have died, despite a major effort to save them.

"We have got a more accurate count and we can confirm that 380 whales are dead," Tasmania's Parks and Wildlife Service manager Nic Deka said.

"There's around 30 left still alive but the good news is that we have saved 50."

Nearly 500 pilot whales were found stranded on an Australian coast Wednesday in the largest mass stranding ever recorded in the country.

Authorities had already been working to rescue survivors among an estimated 270 whales found Monday on a beach and two sand bars near the remote west coast town of Strahan on the island state of Tasmania.

Another 200 stranded whales were spotted from the air on Wednesday less than 10 kilometers (6 miles) to the south, Tasmania Parks and Wildlife Service Manager Nic Deka said.

"From the air, they didn’t look to be in a condition that would warrant rescue," Deka said. "Most of them appeared to be dead."

Tasmania is the only part of Australia prone to mass strandings, although they occasionally occur on the Australian mainland.

Australia's largest mass stranding had been 320 pilot whales near the Western Australia state town of Dunsborough in 1996.

The latest stranding is the first involving more than 50 whales in Tasmania since 2009.

"In Tasmania, this is the biggest (mass stranding) we’ve recorded," Marine Conservation Program wildlife biologist Kris Carlyon said.

Rescue crews remained optimistic about freeing more whales, Carlyon said.

With cool weather helping, "we’ve got a very good chance of getting more off that sandbar," he added.

Why the whales ran aground is a mystery. The pod may have been drawn into the coast to feed or by the misadventure of one or two whales, which had led to the rest of the pod following, Carlyon said.

"It’s really likely this was the one stranding event of a big group. This would have been one big group offshore," Carlyon said.

Marine scientist Vanessa Pirotta said there were a number of potential reasons that whales might become beached, including navigational errors.

"They do have a very strong social system, these animals are closely bonded and that’s why we have seen so many in this case unfortunately in this situation," Pirotta told Australian Broadcasting Corp.

And rescuing them doesn't always work "because they are wanting to return back to the pod, they might hear the acoustics for the vocalizations of the sounds that the others are making, or they’re just disoriented and in this case extremely stressed, and just probably so fatigued that they in some cases don’t know where they are, " she added.

In neighboring New Zealand, more than 600 pilot whales washed up on the South Island at Farewell Spit in 2017.