LONDON, Aug. 4 (Xinhua) -- Visitors to Britain's Chester Zoo were astonished when they witnessed the birth of one of the world's rarest animals, an Eastern black rhino.

With just 650 of the rhinos still alive on the planet, the unexpected public arrival of the calf delighted zoo keepers, as well as the amazed audience.

Proud mom Malindi delivered the youngster in front of onlookers after a 15-month pregnancy earlier the week.

A zoo spokesman told Xinhua: "Typically rhinos are born at night but Malindi, a super rare Eastern black rhino, really surprised onlookers when she went into labor at around 12:30 in the middle of a busy summer's day. With just 650 of these rhinos left on the planet, it's a momentous new arrival."

The healthy calf was delivered safely less than half an hour later in what zoo conservationists described as a "very rare and special event" to witness.

The calf was up on its feet within 15 minutes and was seen running around soon after, before returning to suckle from mom.

Tim Rowlands, Curator of Mammals at the zoo, said: "Although it's still very early days, the little one is showing great signs by feeding regularly and mom and calf appear to have bonded very quickly.

"We just hope this little one helps us to raise some much needed attention to this truly magnificent species, and inspires urgent action to protect their future on this planet. We cannot and must not allow this subspecies to become extinct -- a fate which has, tragically, already become of some of its cousins."

The staggeringly low wild number is a result of the illegal wildlife trade, driven by the increasing demand for rhino horn.

Chester Zoo is also fighting for the survival of Eastern black rhino in the field and has long supported conservation efforts to protect black rhinos and continues to fund, and provide expertise, to numerous sanctuaries, partners and wildlife reserves in Africa.