Twenty-nine pilot 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 34 whales and confirmed the number of deaths, down from 31 reported earlier.
Five whales have survived the stranding and the Department of Conservation will attempt to refloat them on the high tide.
DoC says the process can take some time and may not know how successful it is for or several hours.
They said while it is "heartbreaking", whale strandings are a natural phenomenon and Farewell Spit is a high stranding area ofintertidal sand flats.
"Our rangers along with Project Jonah senior medics are on-site providing care to the remaining live whales with the hope of refloating. No additional help is being requested at this time."
A spotter plane will take to the air and search Golden Bay and also along Farewell Spit for any other stranded whales.
DoC is liaising with Manawhenua Ki Mohua to "ensure the deceased whales are treated appropriately".
On Thursday, DoC Takaka operations manager Dave Winterburn said they had 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.