Miners in Angola have unearthed a rare pure pink diamond that is believed to be the largest found in 300 years, the Australian site operator announced Wednesday.

A 170 carat pink diamond - dubbed The Lulo Rose - was discovered at Lulo mine in the country's diamond-rich northeast and is among the largest pink diamonds ever found, the Lucapa Diamond Company said in a statement to investors.

The "historic" find of the Type IIa diamond, one of the rarest and purest forms of natural stones, was welcomed by the Angolan government, which is also a partner in the mine.

"This record and spectacular pink diamond recovered from Lulo continues to showcase Angola as an important player on the world stage," Angola's Mineral Resources Minister Diamantino Azevedo said.

The diamond will be sold at international tender, likely at a dazzling price.

Although The Lulo Rose would have to be cut and polished to realise its true value, in a process that can see a stone lose 50% of its weight, similar pink diamonds have sold for record-breaking prices.

The 59.6 carat Pink Star was sold at a Hong Kong auction in 2017 for US$71.2 million. It remains the most expensive diamond ever sold.