Windhoek (AFP) - A US hunter who paid $350,000 to kill a black rhinoceros in Namibia successfully shot the animal on Monday, saying that his actions would help protect the critically-endangered species.

Corey Knowlton, from Texas, downed the rhino with a high-powered rifle after a three-day hunt through the bush with government officials on hand to ensure he killed the correct animal.

Knowlton, 36, won the right to shoot the rhino at an auction in Dallas in early 2014 -- attracting fierce criticism from many conservationists and even some death threats.

He took a CNN camera crew on the hunt to try to show why he believed the killing was justified.

"The whole world knows about this hunt and I think it's extremely important that people know it's going down the right way, in the most scientific way that it can possibly happen," Knowlton told the TV channel in footage released Wednesday.

"I think people have a problem just with the fact that I like to hunt... I want to see the black rhino as abundant as it can be. I believe in the survival of the species."

Since 2012, Namibia has sold five licences each year to kill individual rhinos, saying the money is essential to fund conservation projects and anti-poaching protection.

The only rhinos selected for the hunts are old ones that no longer breed and that pose a threat to younger rhinos.

The International Union for Conservation of Nature (IUCN) says there were about 850,000 black rhinos alive through much of the last century before hunting left only about 2,400 in 1995, but numbers have since edged up to about 5,000.

"These are incredibly majestic creatures, and their worth alive is far greater than (when) they are dead," said Azzedine Downes, of the International Fund for Animal Welfare (IFAW), one of the conservation groups opposed to the hunt.

Both black rhinos and the more common white rhino have recently suffered from soaring poaching in South Africa's Kruger Park where hundreds are killed each year for their horns which are used in traditional Asian medicine.

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The exact location of Knowlton's hunt was kept secret to avoid tipping off poachers.

Television footage showed Knowlton accompanied by a professional hunter and local trackers as they tried to find a rhino that was approved for killing.

His first shots injured the animal before he fired the fatal bullets.

"I felt like from day one it was something benefiting the black rhino," Knowlton said just after the hunt ended, his voice croaking with emotion.

"Being on this hunt, with the amount of criticism it brought and the amount of praise it brought from both sides, I don't think it could have brought more awareness to the black rhino."