Tasmania's environment department said 21 stranded dolphins had died and 136 were still alive as of Wednesday morning.

They appeared to be members of a large dolphin species known as false killer whales, officials said, named for the orca-like shape of their skull.

The dolphins were stranded on a beach near the Arthur River inlet on the west coast of Tasmania, a sparsely populated area known for its windswept coastline.

"Stranding response in this area is complex due to the inaccessibility of the site, ocean conditions and the challenges of getting specialist equipment to the remote area," the environment department said in a statement.

A team of wildlife rescue experts and veterinarians has been dispatched to assess the dolphins.

False killer whales can reach up to six metres (20 feet) in length and are known as a highly social species that gathers in pods of 50 or more.

They are frequently involved in mass strandings that can "wipe out whole schools involving hundreds of animals", according to the Australian Museum.