Huge 2492-carat diamond uncovered at Botswana mine

One of the largest diamonds ever found has been unearthed at a mine in Botswana, and the African country's government will put it on show.

The government believes the huge 2492-carat stone is the second biggest ever brought out of a mine.

Canadian mining company Lucara Diamond Corp said on Wednesday it recovered the "exceptional" rough diamond from its Karowe Mine in Botswana.

Lucara said it was a "high-quality" stone and was found intact.

It was found using X-ray technology.

"We are ecstatic about the recovery of this extraordinary 2,492-carat diamond," Lucara president and CEO William Lamb said in a statement.

The weight would make it the largest diamond found in more than 100 years and the second-largest ever dug out of a mine after the Cullinan diamond discovered in South Africa in 1905.

The Cullinan was 3106 carats and was cut into gems, some of which form part of the British Crown Jewels.

A bigger black diamond was discovered in Brazil in the late 1800s, but it was found above ground and was believed to have been part of a meteorite.

The newly discovered diamond will be presented to the world at the office of Botswana President Mokgweetsi Masisi, the Botswanan government said.

Masisi will be one of the first to view it.

The government said it was the largest diamond found in the southern African country, which is the second-biggest producer of diamonds and has unearthed all of the world's biggest stones in recent years.

The Karowe Mine has previously produced four diamonds over 1000 carats.

Before this discovery, the Sewelo Diamond, which was found at the Karowe Mine in 2019, was recognised as the second-biggest mined diamond in the world at 1758 carats.

It was bought by French fashion house Louis Vuitton for an undisclosed amount.

The 1111-carat Lesedi La Rona diamond, also from Botswana's Karowe Mine, was bought by a British jeweller for $US53 million ($A79 million) in 2017.

Natural diamonds are at least a billion years old and some of them more than three billion years old, scientists say.