A giant diamond named the "Pink Star" broke the world record for a gemstone sold at auction when it fetched $71.2 million in Hong Kong on Tuesday.

"Sotheby's Hong Kong is very proud to have this record," its Asia chairman Patti Wong told AFP, adding this was a new world auction record for any type of jewel.

Sotheby's worldwide chairman for international jewellery David Bennet, who presided over the auction, called it a "historic sale".

Bidding started at around $56 million. The sale lasted for five minutes before the winning offer came from a phone bidder and prompted a round of applause.

The sparkling oval-cut rock measures 2.69 by 2.06 centimetres (1.06 by 0.81 inches) and weighs 11.92 grams (0.026 pounds).

It was discovered in a mine in Africa by De Beers in 1999.

At a previous auction, in Geneva in 2013, the stone fetched $83 million.

But Sotheby's was forced to take back the flawless diamond after that buyer, a New York-based diamond cutter, defaulted on the sale.

The previous record for a jewel successfully sold at auction was $57.54 million in May 2016 for the 14.62-carat "Oppenheimer Blue" sold by Christie's in Geneva.