A huge gemstone that could become the world’s largest polished round diamond has been found at the Letseng Mine, owned by Gem Diamonds, in Lesotho, southern Africa.

The diamond weighs 478 carats and is the twentieth largest ever found. Gem Diamonds said initial examination suggests it has a flawless center and could produce a 150-carat round-cut white diamond worth tens of millions of dollars.

"Preliminary examination of this remarkable diamond indicates that it will yield a record-breaking polished stone of the very best color and clarity," the company's Chief Executive Clifford Elphick said in a statement.

The stone would dwarf the 105-carat Kohinoor in Great Britain's Crown Jewels. The largest rough diamond found was the Cullinan, in 1905, which weighed 3,106 carats uncut.