More than 400 whales have stranded themselves on a New Zealand beach

More than 400 whales have stranded themselves on a New Zealand beach, with about three quarters dying in what authorities are describing as one of the worst whale stranding they have ever seen.

The pilot whales were found on Friday at remote Farewell Spit at the northern tip of the South Island.

The area seems to confuse whales and has been the site of previous mass stranding.

Department of Conservation community ranger Kath Inwood said about 300 volunteers had joined conservation workers on the beach.

She said they had refloated the whales at high tide and had formed a human chain to try and prevent them from swimming back ashore.

"It can be really quite distressing seeing so many dead whales," Ms Inwood said.

"People need to be resilient and handle that and then get on with what needs to be done."

She said volunteers had earlier tried to keep the surviving whales damp and cool by placing blankets over them and dousing them with buckets of water as they waited for the tide to rise.

The high tide allowed volunteers one chance to help the whales.

Should the whales become stranded again, the volunteers would have to wait until the next daylight high tide on Saturday.