Between 20 to 30 whales have stranded in Golden Bay, near the top of the South Island.
Project Jonah received reports of a pod of whales coming onshore about 7pm Saturday.
Local medics were on site, and the senior Project Jonah team was en route.
General manager Daren Grover said they would stay with the whales until last light.
Crews were expected to return to the beach just before 6am Sunday.
It is the third stranding in the area in the past two months.
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