The tigers pounced on the 32-year-old contract cleaner after he jumped into the moat surrounding their enclosure and then moved toward the animals, the zoo said in a statement.

The zoo, one of Singapore's most prominent tourist attractions, described the victim as "apparently disturbed and agitated".

Fellow workers reported that he "was acting a little bit erratic and odd, throwing papers around" before the incident, assistant director of zoology Biswajit Guha told Singapore's 938Live radio.

Guha said the cleaner worked at the chimpanzee area and was on his lunch break when the tragedy occurred.

"Goodbye, I won't be seeing you again," Guha quoted the victim as telling one of the zookeepers.

"And they saw him riding off on a bicycle and coming back in through the front entrance again, and then about five minutes later, the whole alert came on the walkie talkie," he said.

Horrified visitors screamed as zookeepers rushed into the tiger enclosure to try to rescue the victim.

They threw rocks to try to distract the animals, which dragged their victim toward a passageway, said Guha.

Zoo workers finally succeeded in luring the tigers away from the man and confining them to their pens, but paramedics later pronounced him dead.

The victim had injuries mainly to his head and neck, Lieutenant Colonel N Subhas, the director of public affairs with the Singapore Civil Defence Force, told AFP.

The zoo identified the dead man as Nordin Bin Montong, a zoo contract worker from Malaysia.

"At no time was any visitor or Singapore Zoo staff exposed to any danger," the zoo said.

Police said they were called to the zoo about 12.30pm (3.30pm AEDT) and were investigating the "unnatural" death.

The zoo said the moat and other permanent safety features at the enclosure meant there was no risk to visitors or staff.

"Nonetheless, we have temporarily closed the white tiger exhibit to visitors to facilitate investigations into this unfortunate incident," it said.