GLOBAL numbers of a critically-endangered species have been boosted with the birth of two rare Eastern black rhino calves at Chester Zoo.

They were delivered safely onto soft sand following pregnancies lasting around 15 months.

Incredible CCTV footage shows the birth and adorable wobbly steps of the first calf, with the youngster getting to its feet only minutes later.

The first was born to 20-year-old mum Kitani on Monday, June 19. The second arriving this Monday to 10-year-old Zuri.

Their births take the number of Eastern black rhino at the zoo to 10 and mark important success stories in an acclaimed breeding programme for the highly threatened species.

It is believed less than 650 now remain across Africa and the International Union for the Conservation of Nature lists the animals as critically endangered in the wild.

Tim Rowlands, the zoo's curator of mammals, said: "These two births are a magnificent boost to the endangered species breeding programme and offer new hope for these wonderful animals.

"Eastern black rhinos are one of the world’s most high profile species, teetering on the brink of extinction in the wild.

"We cannot underestimate how important these animals are to the future of their species.

"Kitani has bonded well with her calf during these important early days and is doing a very good job so far, as is Zuri who is also an experienced mum.

"The whole team is overjoyed and we now hope that these little ones help create more awareness of the plight of their cousins in the wild."

A huge surge in illegal poaching, driven by a global increase in demand for rhino horn to supply the traditional Asian medicine market, has resulted in around 95% of rhinos being wiped out since the turn of the 20th century.

The in-depth specialist knowledge developed by the zoo’s keeping and science teams running the rhino breeding programme is being used right now in Africa to boost conservation efforts in the field.

Mike Jordan, Chester Zoo collections director, said: "It's superb to see the new calves taking their first steps; as we consider that each and every rhino calf is so important to the future of the species.

"We are one of a number of conservation organisations working in Africa - including Save the Rhino International and the International Rhino Foundation - to ensure the long-term survival of both black and white rhinoceros in the wild.

"Alongside that, it’s vitally important to have a healthy breeding programme in zoos to maintain a genetically viable safeguarded population which is helping to develop the husbandry and scientific expertise that our teams can transfer to the wild.

"Conservation is critical, which is why these youngsters are absolutely vital."