A whale protection group says the condition of a stranded whale meant putting it down was the only humane option.
The gray's beaked whale had been in waters off Whangaparoa Peninsula north of Auckland for about three weeks before it beached on Saturday.
Kimberly Muncaster of Project Jonah says unfortunately the whale was in poor condition and the kindest thing was to put the animal down.
She says a marine mammal biologist who checked the whale found it was extremely emaciated.
Ms Muncaster says the whale may have been sick before it stranded, but it was hard to tell because so little is known about rarely-seen gray's beaked whales.