(CNN) Desperate efforts are underway to save dozens of pilot whales still alive after hundreds stranded themselves on a New Zealand beach, in the third largest mass stranding in the country's history.

At least 250 whales were already dead of 400 found beached on Farewell Spit in Golden Bay on the tip of the South Island Friday, the Department of Conservation said in a statement.

Rescuers attempted to refloat more than 100 whales mid-morning, of which about 50 returned to sea.

However, another 80 to 90 whales who were freed re-stranded themselves in the same place just five hours later, Inwood said.

Hundreds of volunteers have come out to help the pilot whiles, pictured here at high tide.

Volunteers swoop on site

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