More pilot whales were expected to die last night as dry weather and nightfall hampered efforts to save a big pod that became stranded on Farewell Spit.
Andrew Lamason of the Department of Conservation (DoC) said up to 500 volunteers could be needed at Golden Bay, near Nelson, to help get a group of 174 whales back in the water today.
Initial estimates of 30 stranded pilot whales rose yesterday to 60, then 143, and finally 198.
Mr Lamason said of those, two dozen had died by 6.30pm and he expected that number to rise.
DoC was scaling down the rescue operation as night approached.
"We can't have people overnight in the water with whales. It's just far too dangerous," Mr Lamason said.
To have a good chance of survival, stranded whales needed overcast or rainy conditions, but Farewell Spit had experienced dry, sunny conditions yesterday.
"This is a big stranding. It's a real challenge."
People had to brace themselves for the unpleasant possibility the pilot whales would have to be euthanised, but rescuers were a long way from giving up on the animals.
"We'll just keep on trying."
The high tide today just before dusk would be a good chance to refloat the pod, he said.
Mr Lamason said the geography of Golden Bay - a big shallow hook - meant it was often the site of strandings.
"Things come in, they get disoriented, and unfortunately we end up with a lot of dead whales."