One person was killed and two others were injured Tuesday at San Francisco Zoo when a tiger escaped from its cage and attacked Christmas Day zoo visitors, according to a newspaper report.

The tiger was shot dead by police officers while it was attacking visitors, a fire department spokesman was quoted as saying by the San Francisco Chronicle newspaper at its website.

Officials said the attack happened shortly after the zoo's 5:00 p.m. closing time at a cafe on the east end of the zoo.

The tiger cages are located near the center of the zoo and it was still not clear how the tiger escaped. Police said they were investigating the incident.

Zoo officials at first worried that four tigers had escaped, but three of the tigers never left their pen, according to Ken Smith, the spokesman of San Francisco Fire Department.

The condition of the two injured people was not immediately known.

Tuesday's killing at San Francisco Zoo happened almost exactly a year after a zookeeper was mauled by a tiger during a public feeding. The California state authorities have ruled that the zoo was responsible for that incident because of the unsafe configuration of the cages.