Nearly 200 pilot whales have been stranded on a notorious New Zealand beach, which is renowned as a deathtrap for the marine mammals, officials say.

Two dozen whales from a pod of 198 had been already dead on Friday as rescuers continued efforts to save the creatures found stranded on Farewell Spit beach at the northern tip of New Zealand's South Island, said Andrew Lamason, the area manager for the Department of Conservation.

Many conservation workers, including those from Project Noah, and volunteers are attempting to refloat the whales during the high tide.

“Re-floating stranded whales is a difficult and potentially dangerous job... community group Project Jonah has 140 volunteers in the Golden Bay area who are trained to do this and we're working alongside them,” Lamason added.

Experts say the task may take a few days due to the vast number of animals stranded.

Cetacean stranding is a common phenomenon in Farewell Spit beach with at least eight cases reported during the past decade.

In January last year, two cases of mass stranding were recorded within the space of a week.

Mass strandings have baffled scientists, with some speculating that healthy whales beach themselves while trying to help sick or disorientated family members.

Meanwhile, the topography of certain places, such as Ocean Beach in Tasmania, Geographe Bay in Western Australia, and Golden Bay in New Zealand, may somehow scramble the whales' sonar navigation, causing them to strand en masse.

Stranded whales are vulnerable to dehydration and sunburn until rescuers take advantage of high tide and move them back into deeper water.

They sometimes die because their body collapses under its own weight, or drown when high tide covers their blowhole. Refloated whales often swim back ashore and have to be euthanized.

Pilot whales, the most common species of whale in New Zealand waters, reach a body length of approximately seven meters and may weigh up to 3,000 kilos.

GMA/AS