About 100 pilot whales and bottlenose dolphins have died in a mass stranding on the remote Chatham Islands, about 800 kilometres off New Zealand’s east coast.

Most of them were stranded at the weekend but rescue efforts have been hampered by the remote location of the island.

New Zealand’s Department of Conservation said 97 pilot whales and three dolphins died in the stranding, adding that it learned of the incident on Sunday.

“Only 26 of the whales were still alive at this point, the majority of them appearing very weak, and were euthanised due to the rough sea conditions and almost certainty of there being great white sharks in the water which are brought in by a stranding like this,” DOC Biodiversity Ranger Jemma Welch said on Wednesday.

Mass strandings are reasonably common on the Chatham Islands. One of the biggest strandings occurred in 1918, with up to 1000 animals dying.

Mass whale strandings have occurred throughout recorded modern history, and why it happens is a question that has puzzled marine biologists for years.

In late September, hundreds of whales died in shallow waters off western Tasmania in one of the world’s biggest mass whale strandings.

-AAP