A total of eight people have been injured after a tree "unexpectedly broke and fell” - with one of them fighting for their life.
The horror accident happened at around 2.05pm local time (7.05pm GMT) on Wednesday afternoon as hundreds of families and visitors were visiting San Antonio Zoo, in Texas, US.
Staff members quickly rushed to the victims after there was "a lot of blood at the scene", according to one eyewitness whose daughter was hit by the branch.
Emergency services were called to the zoo and transported all of the victims to hospital following their injuries.
Joe Arrington, spokesman for San Antonio Fire Department, confirmed one the injured guests was quickly transferred to a nearby hospital as a Priority 1 - which means the victim has suffered a life-threatening injury.
In a post on Facebook, Kelly Evans Bailey, whose daughter was alleged to have been injured by the tree, said there was "a lot of blood at the scene."
She wrote: "I'm asking for big prayers for Jordyn and all of us. At the San Antonio Zoo this morning a large tree fell on us as we were walking.
"We are at the hospital now, been here for hours. Can't post all the details now, but Jordyn has been put to sleep for now so they can run tests.
"Me and Caleb and Lee got some scrapes and bruises. I'm pretty sore but so scared for my baby girl.
"Please pray she comes out okay. There was a lot of blood at the scene, it all happened so fast there was no time to react. This all just feel so surreal.."
Hope Roth, vice president of marketing for the San Antonio Zoo, said the zoo was packed full of families enjoying a sunny day out when the frightening accident happened.
She said: “It’s such an unfortunate situation and a busy spring break day at the zoo."
The other six victims conditions remain unknown and the ages of the victims have not been released.
It's not the first time the zoo has been plagued with incidents after a clouded leopard named Nova escaped from its fence on January 13.
Officials said the enclose had been "intentionally cut" as staff scrambled to get the animal back .
The zoo was forced to shut during the day-long search for Nova who was eventually returned.
Staff and customers were unharmed and the zoo reopened the following day.
