A man was mauled to death by three tigers after breaking into their enclosure at a zoo in Copenhagen, police and staff at the zoo say.

The victim, a 20-year-old Afghan who was given Danish nationality last month, was found lying on the floor by employees at the zoo about 5.30am local time (5pm AEST) on Wednesday.

"He was attacked by the three tigers. He was found lying on the ground," police spokesman Lars Borg said.

Police said they do not know why the man broke into the enclosure and are appealing for witnesses.