The growing black market in wildlife has become the world's third biggest source of criminal income after drugs and guns, experts say.

"Quantifying levels of wildlife crime has never before been possible," Remi Chandran, research associate at the United Nations University, said in a statement.

The international police agency Interpol says on its website that the true value of illegal wildlife trade may never be known as much of it occurs in less developed parts of the world, but that it may be significantly higher than the US$20 billion estimate.

The new UN database, supported by the International Fund for Animal Welfare, is intended to improve on Interpol's own database, which relies on information submitted by national authorities and is only shared among them.

Interpol praised the new model as promising and said it would consider using it.

The project will raise awareness about the black market in animals and plants by sharing information with the public, not just with governments, the statement said.

The new database system was presented on the sidelines of a June 3-15 meeting of the 171-nation Convention on International Trade in Endangered Species (CITES) in The Hague.

Contraband, from elephant ivory to the organs of endangered tigers, can sell for more than its weight in gold, driven mainly by Chinese demand that has surged in line with the country's expanding economy, scientists and environmentalists say.

Rare breeds have been decimated because of demand not only from China but also from Westerners wanting alternative treatment with products made of tiger bone, rhino horn and bear bile.