The world's tallest animal, the giraffe, comprises a group of species rather than just one, a study finds.

Giraffes have long been considered to represent a single species classified into various subspecies.

But a new study has revealed that that at least six species of giraffe amble across Africa.

The research, which was recently published in the journal BMC Biology, was supported by the Wildlife Conservation Society (WCS).

Lead researcher David Brown, of the WCS, said: "Some of these giraffe populations number only a few hundred individuals and need immediate protection.

"Lumping them all into one species obscures the reality that some kinds of giraffe are on the very brink."

The WCS hopes that classifying current subspecies as fully fledged species will help conservationists to save the most endangered populations.

These include the reticulated giraffe (currently the Giraffa camelopardalis reticulata), the Nigerian giraffe (currently the Giraffa camelopardalis peralta) and the Rothschild giraffe (currently the Giraffa camelopardalis rothschildi).

These three populations inhabit distinct regions of Africa and number only 3,000, 160, and a few hundred individuals, respectively.

According to the WCS, giraffe numbers have seen a worrying 30 per cent decline over the past decade. Less than 100,000 giraffes remain across Africa, the WCS added.

The giraffe genetic study was a collaboration between the University of California, Los Angeles, Omaha’s Henry Doorly Zoo and the Mpala Research Centre in Kenya.

Male giraffes can be 4.8 to 5.5 metres tall and weigh up to 1,300 kilograms. The record-sized bull was 5.87m tall and weighed approximately 2,000 kg. Females are generally slightly shorter, and weigh less than the males do. The giraffes’ range extends from Chad to South Africa.