An extremely rare postage stamp is likely to fetch $25,000 at auction today in Wellington.

When Queen Elizabeth II's father King George VI's 1949 visit to New Zealand was cancelled, due to ill health, the Post Office ordered all 'Vanguard' stamps be incinerated.

Auctioneer John Mowbray said the first surviving stamp surfaced about 1976.

He said everyone knew about the design and the stamps being destroyed, but no one knew there were any left.

Mr Mowbray said someone would have gone to jail if they had been caught keeping stamps back from the furnace.

"The belief is that at the time of incineration, a few stamps were put in the pocket of one of the people responsible for doing it, and it's these seven stamps that exist."

The first stamp sold for about $14,000.

Mr Mowbray said the condition of the seven stamps "varies markedly because of the way they've been handled", and some are in "very poor condition".

He said the stamp in today's auction is the finest of the seven.