100 pilot whales dead after New Zealand stranding

More than 100 pilot whales that stranded on a New Zealand beach have died, conservation officials said on Saturday, voicing grave fears for more than 90 others from the pod.

The whales beached themselves on Friday at Farewell Spit at the northern tip of the South Island, with dozens of rescuers racing to re-float the marine mammals on the evening high tide.

But Department of Conservation (DOC) spokesman Andrew Lamason said the whales had swam aground again overnight after being shepherded out to deep water.

"We've now got 103 that are confirmed dead and we're trying to keep the rest alive," he told AFP.

"There's about 150 volunteers trying to make them as comfortable as possible, they're putting sheets on them and water over them.

"But we're preparing ourselves for a pretty bad outcome, each time they re-strand their health goes down quite dramatically."

Lamason said the incident was distressing for all involved.

"There's a lot of young ones out there that have already passed away. It's been quite an emotional time for our staff," he said. "The whales also go through a lot of physical and emotional trauma."

He said another attempt at refloating would be made at high tide late Saturday, but if that failed then euthanasia would be discussed.

Farewell Spit beach, about 150 kilometres (95 miles) west of the tourist town of Nelson, has been the scene of mass pilot whale strandings in the past.

There have been at least eight in the past decade, including two within the space of a week in January last year, although the latest stranding is one of the largest.

"It seems to happen each summer," Lamason said. "It's highly likely it's the geography, potentially they're coming in here hunting for fish and becoming disorientated and dying.

"It could be that some of the pods are sick and that brings them up onto the beach, we don't really know."

Pilot whales grow up to six metres (20 feet) long and are the most common species of whale in New Zealand waters.