Only 11 of 32 whales that stranded on the West Coast are still alive, The New Zealand Herald reports.
The pilot whales stranded at the mouth of the Okuru River, south of Haast yesterday afternoon.
A Department of Conservation spokeswoman said it looked like the whales had been there about 12 hours when staff arrived.
"DoC staff, Makaawhio Iwi members and local people cared for whales but some weren't able to be reached.
"A refloat of the whales wasn't possible because of dangerous sea conditions, with a high swell, and because the tide was receding. It would have been too dangerous to carry out a refloat of the whales in darkness in the overnight high tide."
Pilot whales often strand in large numbers,DoC's website said.