All 28 pilot whales stranded near Golden Bay have been killed.
The whales were discovered stranded on Farewell Spit on Thursday morning, above the high tide mark. Twelve were dead.
The Department of Conservation says they were too weak for a rescue to be attempted.
DoC says the whales could have attracted others in their pod to Farewell Spit, prompting a bigger stranding. Pods commonly comprise up to 200 whales.
The whales will be measured and left to rot.
AAP reports pilot whales regularly strand themselves on New Zealand shores, especially from November - March.
Strandings are common along Farewell Spit, which is 24km long. Whales often beach themselves again after being refloated.