A 12-metre humpback whale has died overnight in the Firth of Thames after a report it had been stranded in Kaiaua on Thursday.

The Department of Conservation received a call about 7pm and had a response team on site by 9pm, a statement said.

Iwi, local volunteers and a member of the fire brigade joined the team to keep the whale comfortable.

Although the whale was alive when the team arrived, it was thought to have died just before midnight.

The whale's cause of death was unknown, so samples were being taken for genetics, toxicology and stable isotope analysis, a DOC spokeswoman said.

She said DOC was working with iwi on plans to bury the humpback whale.

"It will be buried before it starts to decompose," she said.

-Stuff/Kendall Hutt