A plum-sized diamond known as the “Pink Star” has been auctioned in Geneva for $A89.51 million, a world record for a gemstone.

David Bennett, chairman of Sotheby’s jewellery division in Europe and the Middle East, brought down the hammer in a Swiss hotel after an intense, five-minute bidding race.

The winning bidder, a bearded man apparently in his sixties sporting a skullcap, was pitted in a one-on-race against a telephone competitor.

The bidding in Geneva was conducted in Swiss francs, starting at 48 million and working its way upwards million-by-million.

There was a long silence as the price reached 67 million Swiss francs, before the in-room bidder came back with the winning 68 million.

Commission included, the final price was 76 million francs – the equivalent of $A89.51 million.

There were up to 150 people in the auction room who erupted into applause as the theme tune from the Pink Panther was played as a tongue-in-cheek gesture.

The winning bidder declined to identify himself but confirmed that he had been representing another individual, whose name and location he refused to reveal.

The diamond had been estimated at $A64.71 million.

Three years ago, Sotheby’s set an auction record of $US46.2 million ($A49.82 million) – commission included – for a diamond when it sold the Graff Pink gemstone.

Sotheby’s later identified the buyer as Isaac Wolf, a New York diamond cutter.