Almost 600 pilot whales have stranded themselves off a remote coastline in New Zealand over the past few days in a mass stranding, leaving rescuers struggling to save them.

By Sunday about 335 of the whales were dead, 220 remain stranded, and 100 were back at sea, the Department of Conservation said.

On Friday morning the department discovered 416 pilot whales had stranded themselves at Farewell Spit in Golden Bay at the top of the South Island, with more than 70 per cent dead by dawn.

But two additional pods also stranded themselves in the same area over the weekend.

On Sunday 17, pilot whales that were part of a large pod that stranded on Saturday near Puponga were successfully turned around on the high tide and sent back into deeper water in Golden Bay.

Two boats were used to guide the whales out to rejoin the original pod, with rescuers hoping that the whales will find a way into deeper, safer waters.

Some of the deceased animals have been found with shark bites, and volunteer rescuers have been warned about the possibility of stingrays and sharks.