The Duke of Cambridge spoke out earlier today after visiting a Chinese elephant sanctuary on his final day of his trip to the far east.
In a rare rebuke aimed at citizens in the host nation, the second-in-line to the throne appealed to end the slaughter of animals for their tusks.
He is a passionate campaigner on the subject and called the trade a "vicious form of criminality."
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Prince William with Ran RanGETTY IMAGES
Prince William fed Ran Ran carrots
Picture of ivory ornamentGETTY IMAGES
An ivory ornament, commonplace in China
On the last day of his visit to the region, he said: "Ending demand for ivory is down to citizens across the world.
"No tradition or fashion is worth the extinction of an entire species, and no criminal gang should be allowed to destroy any part of nature."
"I am sure there are millions of people who share this conviction."
Wiliam with Ran Ran and Xiong ChaoyongGETTY IMAGES
Wiliam with Ran Ran and Xiong Chaoyong
You're going to get a runny tummy.
China is a huge consumer of ivory and the trade in the animal product threatens wild elephants with extinction as poachers feed the demand in the Far East.
Prince William added: "It is appalling that elephants - and many others - may be extinct in the wild in our lifetimes, and that we seem to be hurtling towards that tragic outcome.
"The extinction of animals such as elephants, rhinos and pangolins would be an immeasurable loss to the whole of humanity."
William with Ran RanGETTY IMAGES
William and Ran Ran, 13
The Prince has campaigned with David Beckham and Chinese basketball star Yao Mingto to stop the trade in products from endangered animals.
When Prince William met Chinese president Xi Jinping earlier this week the matter of ivory trading was raised.
Picture of seized tusksPHILLIPE LOPEZ&AFP&GETTY IMAGES
Tusks seized in Hong Kong last year
Charlie Mayhew, founder and chief executive of the wildlife conservation organisation Tusk Trust which has the Duke as its patron, said he believed Prince William's stance could make a difference.
He said: "I think what we've just heard is a really powerful speech appealing to the Chinese people following on from a very constructive meeting that I gather he had with the president on this issue.
"Just think about it - in the last four months he has raised this issue not only with the president of China but the president of the United States - I don't know anybody else who has managed to do that in years."
Prince William with young conservationistsPA
The Duke of Cambridge and young conservationists
The Duke visited the Xishuangbanna nature reserve where around 250 of the animals live in the wild in the sanctuary.
He met one of them, Ran Ran, a 13-year-old female, who was discovered in a jungle river in 2005 with a leg wound caused by a trap, baskets of carrots.
He rubbed her trunk and gave her a scratch between the eyes as Xiong Chaoyong, the animal's keeper, handed carrots from a basket to the Duke which were gratefully taken by Ran Ran.
Prince William kept feeding and at one point the elephant's mouth was crammed full while she still had her trunk wrapped around another four carrots.
The Duke told Ran Ran "you're going to get indigestion" and after another basket full of carrots was quickly eaten, added: "You're going to get a runny tummy."
Prince William also met with conservationist and wildlife photographer Xi Zhinong, who showed him pictures he had taken of animals, such as monkeys, cranes and the endangered pangolin.
The Duke told him: "What you do with your pictures is to help education and conserve the natural world for the next generation. Your work is remarkable.
"The quality of your work is such that it must take a lot of patience to achieve."
He also met young rangers who were painting a model elephant and they asked William to join them.
Picking up a brush, the Duke said: "I hope you know that the future of these animals are down to your generation. You are the ones that are going to have to speak up."
Pic of Prince William with wildlife photographsPA
The Prince saw pictures taken by Chinese conservationist Xi Zhinong
Prince William's visit came at the end of a seven-day tour of Japan and China and in an impromptu meeting with the British press he said he had enjoyed his trip.
Speaking at Xishuangbanna he said: "I've had a truly wonderful visit to Japan and China. I've met lots of wonderful people - a very warm reception, and I really enjoyed myself.
"I look forward to building on relationships and building on partnerships going forward and doing as much collaboration as possible in a number of areas. "But it's been very enjoyable and I have had a great time."
Prince William was not joined by his wife Kate, who is expecting a younger sibling for Prince George next month.