Prime Minister John Key's signature on a bottle of pinot earned $25,000 for mayoral candidate and Labour MP Phil Goff, but the PM has no idea how Goff got the bottle.

The bottle of pinot noir was auctioned with another bottle signed by Labour leader Andrew Little at a fundaising dinner for Goff. The lot contributed $25,000 to Goff's campaign.

A spokesman for Key said the Prime Minister had not signed a bottle for Goff's campaign.

"The Prime Minister regularly signs items to be auctioned. He didn't sign a bottle of wine for Mr Goff's campaign on this occasion, therefore it's likely someone re-donated it."


"As the Prime Minister has said, he will have to work constructively with whoever is elected mayor of Auckland and therefore has not endorsed any candidate."

A spokesman for Goff's campaign confirmed it was not from Key but did not know who had donated it.

He said all donations of more than $1500 would be disclosed as required after the election.

The bottle was not one of Key's own PM's Pinot label, which Key dispenses as gifts and donations for auctions.

Goff is standing as an independent rather than on the Labour ticket but Labour MPs have spent time campaigning with him including Jacinda Ardern and Phil Twyford.

While the Labour Party itself only declared $287,000 in donations last year, Goff's team managed to almost match that in one dinner getting $250,000.

About 350 people attended the dinner for the Chinese community at the Imperial Palace restaurant in Ellerslie where tables sold for $1680 each.

Organised by former Labour MP Raymond Huo, the star lot was a book, The Governance of China, written and signed by Chinese President Xi Jinping. That sold to a phone bidder from China for $150,000.