The whale got stuck on a sandbar in the shallow estuary at Moncks Bay in the south-east of the city.
It was hoped the whale could be refloated at high tide shortly before 8am today, but rescue organisation Project Jonah said the whale died about 3am.
Members of the rescue organisation stayed at the scene overnight, with the Department of Conservation and Coastguard Sumner, but it was too dark, and the tide too low to look at whether the whale could be refloated.
Volunteer Jessica Halsey said on Sunday there were lot of people around asking questions, but they had cleared away as it got darker.
Officials had not been able to identify the type of whale it was, or the possible reason it had got stranded, she said.
This whale beaching comes a week after a pod of 45 false killer whales and one bottlenose dolphin were euthanised after becoming stranded near Māhia.
A sperm whale stranded on South Brighton Beach in Christchurch died overnight on November 5.
