Auction house says engraved silver, which has a reserve of $325,000, is a proud moment of friendliness in Australian history.
Descendants of a slain Ngapuhi chief fear that a re-discovered taonga that was lost for more than 200 years will be gone for good after an auction last night.
The engraved silver medal was given to Bay of Islands chief Te Pahi by Philip Gidley King, the third governor of New South Wales, in 1806.
It was auctioned in Sydney - reportedly for A$300,000 ($325,000) - despite efforts by the chief's descendants to halt proceedings.
Te Pahi's relative Hugh Rihari said nothing was known of the medal's whereabouts until it resurfaced in Sydney more than 200 years after Te Pahi was killed by British whalers in 1810.
His whanau had considered filing an injunction to halt the auction, and on Monday night some were seen performing a protest haka outside Sotheby's.
But by last night Mr Rihari was resigned to the fact that an important piece of Ngapuhi and New Zealand history would likely be gone.
The buyer's identity was not known last night, but Mr Rihari had earlier said he hoped "our museums" would bid. "We have gone as far as we can but at the end of the day there's not much more we can do."
The Ngati Torehina kaumatua from the Purerua Peninsula said he sought a postponement of the auction so he could have a discussion with Sotheby's but was "flatly refused".
"It's in the hands of people in Australia who have their own rules and regulations for the protection of their objects of cultural significance and they believe that this medal is of as much importance to them as it is to us here in New Zealand."
Sotheby's chief Gary Singer said before the auction that the reserve on the medal, which was in mint condition and a fine example of colonial silver-smithing, was A$300,000.
The auction was to go ahead because no one could clearly state their links to Te Pahi, he said.
"No one has come forward and said, 'This is the basis of my claim' - when people make a claim they usually back it up," he said
The medal was also an important piece of Australian history and one of its "prouder moments".
"This was an incident where we recognised an indigenous visitor and we have gone out of our way to be friendly and treated him with respect."
Te Pahi received the medal for helping to foster relationships and trade between Maori and the British at the turn of the 19th century.
But he died after an apparent revenge attack for the massacre of the crew of the whaling ship The Boyd at Whangaroa a year earlier.
The medal had been in a family's possession for at least 120 years before it was taken to Sotheby's.
Te Pahi, whose name was Anglicised to Tippahee on the medal, struck up a friendship with Mr King and stayed with him in Sydney for three months.
He was keen on accessing colonial technology and goods while the governor sought protection for whaling crews that were being seen on northern shores with increasing frequency.