A pod of 82 pilot whales has beached in Golden Bay, west of Nelson.
One baby whale and nine others have died, and the others face an uncomfortable night with Department of Conservation (DOC) staff unable to attempt to refloat the whales until tomorrow, DOC spokeswoman Trish Grant said.
Members of the public alerted DOC after finding about 30 whales stranded at 1.30pm at Puponga Point, near the base of Farewell Spit, she told NZPA.
Staff had tried to prevent the other whales from beaching, but were unsuccessful.
About 120 DOC staff and volunteers were working to keep the whales hydrated and protected from the sun this afternoon and did not need any further assistance tonight.
Staff were still assessing the whales' conditions, Ms Grant said.
"It is an ordeal for them to be exposed stranded like that and be exposed in the sun and stuff and unfortunately some just do die. But we make every effort that we can to refloat those that are still surviving.
"We'd be optimistic that there's surviving whales tomorrow that we can refloat."
The next high tide was about midnight but it was too dangerous to refloat the whales in the dark, Ms Grant said.
It was likely a few staff would watch the whales overnight and work would begin tomorrow preparing the whales for a refloating attempt during the next high tide, about midday.
"Not much can be done for the whales overnight. The tide's going to come in and they are likely to move around ... People are going to have to move to a safe location."
Ms Grant was hopeful they would be able to save some of the whales.
Whale strandings were not uncommon in the area, and some whales had been successfully saved, she said.
"Though, some even though they are refloated, do wash up dead later on because they've been through such an ordeal so they are considerably weakened by it."
It was not known why whales strand, but people had theories about it including mistakes in navigation, Ms Grant said.
"It's something that has occurred reasonably often in Golden Bay with pilot whales, and just even the shape of the bay could mean they kind of get a bit caught with the spit coming round, so it could just be navigational error."
Pilot whales are about 4m-6m long. They are the most common species of whale seen in New Zealand waters.
Last month 24 pilot whales died after stranding in Parengarenga harbour, near Cape Reinga in the Far North.
In December 2009, more than 120 whales died in two separate beachings at Farewell Spit and Colville Bay, north of Coromandel.
In December 2006, rescuers managed to save the majority of 140 pilot whales stranded at Puponga Bay.
But just two weeks later, on New Year's Day 2007, 50 whales died after beaching at Farewell Spit.
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