Vitali, one of three Siberian tigers at the Calgary Zoo, was on exhibit Monday morning. (Jeff McIntosh/Canadian Press)

A man is in hospital with serious injuries after sneaking into the Calgary Zoo overnight, scaling two fences and being injured by a tiger.

Two men, both aged 27, jumped a 2.4-metre-high barbed wire fence at about 1 a.m. Monday to enter the zoo.

One of the men then scaled the outer perimeter safety fence around the tiger enclosure, which is just over a metre high. He didn't enter the tiger exhibit, but approached the inside fence where a two-year-old male Siberian tiger was roaming, zoo officials said Monday.

The tiger, named Vitali, may have hooked the man with a claw and pulled an arm inside the fence, said a zoo veterinarian. The second man, who came to his aid, was also hurt.

The men knew a security guard who worked at the zoo and called her on her cellphone for help.

Security personnel took the men to a zoo office where they were both given emergency first aid until medical services arrived. The seriously hurt man was then taken to the Foothills hospital.

Motive unknown

Calgary police are investigating and may lay breaking and entering or trespassing charges against the men. Police are unsure of the motive and don't know if alcohol was involved, said acting Staff Sgt. Rick Halford.

One of the men alleged to have sneaked into the Calgary Zoo is taken into custody on Monday.

"There's no indication that the two offenders were involved in anything else other than just being silly, I suppose," he said.

Grahame Newton, the zoo's director of corporate services, said the second fence, which the men didn't scale, is designed to keep the tigers inside their enclosure. It's 4.5 metres high, with a large overhang and an electric component.

"Certainly we will be reviewing it to see whether there is anything that can be done. But in this case here, I think it just simply appears to be a case of two individuals intent on breaching the security and they did it. Unfortunately it resulted it some very serious injuries."

Tiger to remain on exhibit

The tiger, who wasn't hurt, will remain on exhibit, said zoo curator Tim Sinclair-Smith.

"Vitali has certainly done nothing wrong. It's his natural behaviour," he said. "He will go on display as he always has."

Calgary Mayor Dave Bronconnier defended the zoo on Monday, saying it has a good record of taking care of both animals and visitors.

"You can't foresee absolutely every circumstance. Who could ever predict that somebody would … want to get warm and cuddly with a live animal? Just common sense should tell you that is just something you just don't do," he said.

"If you want to pet live animals, go to Butterfield Acres," Bronconnier added, referring to a local petting farm.