Petra Diamonds has made a discovery of a 29.6 carat diamond, which is one of the rarest and most coveted in the world, at a mine in South Africa.

Experts have said that the rare find could be worth tens of millions of dollars in the global market. The company officials said that the diamond was unearthed at the Cullinan mine near Pretoria in the country. The Cullinan Diamond was also discovered in the same mine in 1905. Petra Diamonds is operating at the mine since 2008. Other discoveries at the mine include 25.5 carat Cullinan blue diamond during the previous year that was sold for $16.9 million while another diamond known as the Star of Josephine, which was found in 2008, was sold for $9.49 million.

Chief executive Johan Dippenaar, "By some margin, this is probably the most significant [blue] stone we've ever recovered. The stones in the last year or so are selling well above $2m per carat. That's not my quote, that's updates in the market."

Petra Diamonds, which is listed in London, has said that it is planning to release figures on production and sales for the six months to December tomorrow.