Johannesburg (CNN) South Africa's first online auction of rhinoceros horn is underway, with more than 500 kilograms up for bid from Wednesday through Friday.

On Sunday, the High Court in Pretoria paved the way for the controversial auction, ordering the minister of environmental affairs to hand over a permit for the sale of 264 rhino horns to breeder John Hume.

Hume, who owns the world's largest private collection of rhinos, has battled to overturn a ban on the sale of horn in South Africa for years.

John Hume, pictured at his Johannesburg ranch in 2015, has obtained a permit to sell 264 horns.

The Private Rhino Owners Association estimates in the eight years the ban has been in place, owners have spent more than $100 million to protect their rhinos. Without the sale of horn, the association argues, the breeding of rhinos would become unsustainable.

But environmental groups say there is no conservation value in the auction, arguing that rhinos shouldn't be seen as livestock.

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