Time was running out tonight for a group of pilot whales to swim back out to sea on the high tide after becoming stranded at Farewell Spit in Golden Bay this morning.
One whale has already died after the 13 whales were beached.
They were part of two pods of pilot whales which made their way onto the spit.
Department of Conservation Takaka ranger Greg Napp said tonight that a high tide had come in more slowly than expected and the whales were only just floating before volunteers and conservation staff had to leave the beach when it got dark.
"The tide's only got deep enough around the whales now so we're just starting to move them together,'' he said at 9pm.
"We're wanting to bring them together before we walk away from them. From past experience, by bringing them together they've got a chance to meld together in a group and sort themselves out and get a leader and all that sort of stuff.
"But we're just running out of time. We're only just managing to move them now and we're going to have to leave them soon.''
If the whales were still on the beach in the morning, a further attempt would be made during the next incoming tide, with high tide expected at 10.30am, Mr Napp said.
It was estimated nearly 70 whales made their way to the south end of the spit this morning. although 13 were stranded, 55 managed to make their way into deeper water.
Last week 27 pilot whales had to be put down after becoming beached at the spit. A further 12 had already died from natural causes after being stranded.
Mr Napp said it was not known why whales tended to strand at Farewell Spit, but suggested the shape of the area's coastline could contribute to the mammals having trouble.
In November 2012, 28 whales died after becoming stranded in the area, and in January that year more than 80 perished after a mass stranding of 99 pilot whales.
"It seems to be a natural whale trap,'' Mr Napp said.