This is the tragic moment before a white tiger at Delhi zoo mauled a young man to death.

Deputy Commissioner of Police M.S. Randhawa has identified the victim as 20-year-old Maqsood.

The National Zoological Park said he was repeatedly warned he should not get too close to the tiger enclosure but ignored advice.

Initially it was believed he had slipped because the barricade to the enclosure was too low but zoo spokesman, Riyaz Ahmed Khan, said the young man had climbed over a fence and jumped 18ft down into the protective moat before he was attacked.

Television footage revealed the tiger approaching Maqsood before it pounced on him and carried him around the island.

Khan said by the time help arrived the man was dead.

"Around 1.30 pm, we were in the reptiles area when we heard loud screams," witness Himanshu told CNN-IBN news channel.

"I ran to the tiger enclosure where we saw that a white tiger had caught the student by his neck and he was writhing in pain. Some children threw small sticks and stones at the tiger.

"He suffered for the next 10-15 minutes but nobody helped him."

The authorities frightened the tiger into a small cage inside the enclosure. The man's body remained in the outdoor enclosure for two hours after the attack.

"The tiger was just being a tiger," said campaigner Belinda Wright, who fights to protect India's dwindling numbers of wild tigers. "An unusual object fell into his domain... He's a wild animal in captivity. It is certainly not the tiger's fault."

The zoo was evacuated and enclosure has been cordoned off while the police investigation continues.

Khan told AFP: "We are trying to find out who this boy was and why he did what he did. The police are here and they are investigating."

White tigers are considered an endangered species and are found in south and east Asia, particularly India.