MARWELL Zoo has suffered one of the most serious blows in its history with the escape and death of a critically endangered Amur leopard.

The animal escaped from its new enclosure into adjoining trees and was darted by general curator Peter Bircher.

The leopard slipped part way down the tree and never regained consciousness, dying soon afterwards on Monday, the zoo announced yesterday.

A post-mortem was held at the Veterinary Investigation Centre at Itchen Abbas near Winchester yesterday, with the results expected soon to establish the cause of death.

An internal investigation is taking place into how Jade, two, was able to squeeze through the narrow gap between the roofing net and tree.

The zoo said there was never any danger to the public as at no stage was the cat on the loose within the park, which was closed to the public.

The official opening of the enclosure, scheduled for Saturday, has now been postponed.

The £187,000 enclosure, which was due to be put into use last Monday, will remain closed until the inquiry is completed.

A zoo spokesman said: "We are all terribly upset and devastated. It was so unexpected. Nothing like this has ever happened before."

Zoo director Mark Edgerley said: "It is a tragedy of international importance in the animal world because of the rarity of the animal. It is an embarrassment that it should get out of a new enclosure that we thought was secure."

There are feared to be only 30-33 Amur leopards left in the wild in Russia and about 100 in European zoos. Only about 80 can breed so the loss of one is a big blow to the gene base.

Jade had been introduced to the enclosure for the first time on Monday. The escape happened within 20 minutes. Mr Edgerley said: "Clearly the animal was motivated by fear of the enclosure.

"It was fear that gave her momentum to get through a gap that we can't get a fist through. It was a freak accident.

"I'm very concerned it happened. We are going back to the drawing board to look at the design."

Jade climbed some 9m up to the top of the enclosure and then sat perched about 15m up the tree. She was darted and tumbled about 4m into a forked branch.

Once staff were sure she was unconscious a cherry picker crane took her to the ground and she was carried to her cage, where she died within about five minutes.

Mr Edgerley said the likely cause of death was either a broken rib puncturing a lung or a paw pressurising her chest while she was unconscious.