Thirteen whales have beached near Farewell Spit, near Golden Bay.
A group of 20 volunteers, including Department of Conservation (DOC) staff, were working to save the group of 13 stranded pilot whales until high tide.
A Fairfax reporter at the scene said many of the volunteers were helping out at a whale stranding for the first time.
DOC staff in boats had successfully saved the other 55 whales from stranding at this stage. DOC ranger Greg Napp said a strong westerly wind was making conditions difficult and the sea rough.
"We will need to assess the sea conditions around 6.30pm to assess whether it will be safe to have people in chest-deep sea water attempting to refloat the whales in this remote location," Napp said.
The whales would need to be refloated before dark, when it became dangerous for people to work in the sea with the animals.
DOC rangers in a boat had been following the whales still offshore but lost sight of them in the choppy sea.
DOC staff will be out at first light tomorrow looking for any whales stranded on the coastline along and south of Farewell Spit.
"High tide was at 9.30 this morning, so the next high tide is 9.30 this evening - which means we have a short space of time to get them floating again," Napp said.
"It's a long time for them to be out in the sun."