The world risks wiping out a new generation of cures for diseases if it fails to reverse the extinction of thousands of plant and animal species, experts warned.

Biodiversity loss has reached alarming levels, and disappearing with it are the secrets to finding treatments for pain, infections and a wide array of ailments such as cancer, they said, citing the findings of a coming book.

Achim Steiner, executive director of the United Nations Environment Programme (UNEP), said more than 16,000 known species are threatened with extinction, but the number could be more.

"We must do something about what is happening to biodiversity," he said at a news conference on the sidelines of the UN-backed Business for the Environment conference.

"Societies depend on nature for treating diseases. Health systems over human history have their foundation on animal and plant products that are used for treatment."

Technological revolution in the 19th and 20th centuries took the focus on finding cures away from nature as pharmaceutical companies relied on technical components to make medicines, he said.

These companies are increasingly turning back to nature as they run out of chemical combinations, he said.

But the world is "losing the intellectual patents of nature before we even have the chance to understand or unravel them," Steiner said.

"This is the tragedy of not understanding biodiversity," he said, adding it would be a "big fallacy" to think that biodiversity is not linked to the phenomenon of climate change.

The book, previewed at the conference, cited the example of the southern gastric brooding frog discovered in the rainforests of Australia in the 1980s. It has since become extinct.

Research on those frogs could have led to new insights into preventing and treating human peptic ulcers which affect 25 million people in the United States alone, according to the authors of the book, "Sustaining Life".

Valuable medical secrets which the frogs held "are now gone forever," the book's key authors, Eric Chivian and Aaron Bernstein, were quoted as saying in a press statement.

The book contains a chapter describing how seven threatened groups of organisms -- amphibians, bears, cone snails, sharks, non-human primates, gymnosperms and horseshoe crabs -- can be valuable in finding cures for diseases.

The Panamanian poison frog, for example, can make pumiliotoxins that may lead to medicines for heart disease, while alkaloids from the Ecuadorian poison frog could be a source for painkillers, it says.

Cone snails produce a compound which has been shown in clinical trials to be a pain reliever for advanced cancer and AIDS patients, according to the book.

David Suzuki, a Canadian scientist and environmental activist, blamed environmental degradation on the world's heavy focus on economic progress.

"We are creating an illusion that everything is fine, and we are getting richer and richer. But we're doing it at the expense of our children and grandchildren... all in the name of economic growth and progress," he said in a keynote address via video conference.

One solution will be to "take our eyes off the economy," he suggested.

"The real bottom line is clean air, clean water, clean soil that gives us our food, clean energy that comes from the sun, and biodiversity. These are ultimately the most important needs that we have to fight for at all cost."

Hundreds of international business executives, government officials, environmentalists and others have gathered for conference.

It was organised by the UNEP and the UN's Global Compact, an initiative which brings companies together with the UN and other agencies to support environmental and social principles.