Africa's rhinos face their worst poaching crisis in decades with organised crime syndicates killing more than 800 in the past three years alone, conservationists say.

The International Union for Conservation of Nature said in Geneva today poaching is on the rise in South Africa, Zimbabwe and Kenya due to well-equipped and sophisticated crime gangs.

Rhinos are hunted as trophies and their horns sell like gold on the black market. Each pound can fetch tens of thousands of dollars in south-east Asia where the horns are thought to have medicinal value.

IUCN scientific officer Richard Emslie said the remaining 24,990 rhinos might decline in numbers "unless the rapid escalation in poaching in recent years can be halted."