Thirty nine whales stranded on Farewell Spit have died or have been put down.
The long-finned pilot whales were first spotted in shallow water off Abel Tasman National Park on Sunday afternoon and the pod eventually became stranded at night.
Twelve died overnight and the rest were euthanised by the Department of Conservation, as they were too high up on the beach and the tide was going out.
DoC conservation services manager in Golden Bay John Mason said was a very tough call.
"It's not a decision we make lightly. We've got a lot of experience in dealing with strandings and we've now got a pretty good idea about when we're likely to be successful and when we're not. And unfortunately in this situation we concluded that we were very unlikely to refloat those animals successfully."
Senior DoC ranger Hans Stoffregen says a very high tide left the pod stranded about 1km from the low tide mark, and 12 had already died by 9am on Monday.
He said there was no possibility of refloating the surviving whales and staff euthanised them as humanely as they could.