Thirty-one whales have died overnight after they became stranded on Farewell Spit on the South Island.
Project Jonah senior medics and Department of Conservation rangers have located the whales and confirmed the number of deaths.
Five whales had survived the stranding and Project Jonah said they were being monitored and assessed to "see if they are candidates for a refloat".
Project Jonah said "no additional help is being requested at this time" and that "our marine mammal medics continue to be on standby, but have not been mobilised".
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A spotter plane will take to the air and search Golden Bay and also along Farewell Spit for any other stranded whales.
DoC Takaka operations manager Dave Winterburn said on Thursday they received reports of a potential mass stranding at 6pm and sent out rangers to investigate.
"It has been reported that potentially more than 30 whales, likely to be pilot whales, have stranded."
On Thursday night in a Facebook post, Project Jonah said it had received reports of the "potential mass stranding".
The organisation said it was working with DoC which had dispatched rangers to confirm the signings.
Last February close to 50 long-finned pilot whales were stranded at the same location. Forty-nine whales died.
In February 2017, an estimated 600-700 whales were beached in the same location. About 250 died while the rest were refloated.
Farewell Spit is located at the northern end of Golden Bay.