A zoo worker is in a critical condition after being attacked by a tiger at Topeka Zoo in Kansas.
It happened at 9.30am local time, shortly after the attraction opened, as horrified visitors looked on.
It is understood that the worker is a female trainer.
The tigers have been put "in holding", zoo official Molly Hadfield told reporters.
Police and emergency services have been called to the scene.
It comes shortly after a number of Sumatran tiger cubs were put on display at the tourist attraction.
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On March 21 the zoo told followers on Twitter that the four young cubs would be going outside for the first time.
The animal which carried out the attack was a male Samatran tiger named Sanjiv, WIBW reports.
The zoo is not planning to punish the animal - who has been at the zoo since August 2017 - in any way, it is understood.
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Ms Hadfield said: "Right now we're still evaluating, the tigers are in holding."
She continued: "The zoo was open, we did shut down for 45 minutes.
"A few people did witness the attack."
She said the zoo keeper was "alert and awake" after the attack, and added: "We are back open, our tigers are in a holding cell, but the rest of the zoo is open."
At the time the animal arrived, Topeka Zoo wrote on Facebook: "Sanjiv, a male Sumatran tiger, joined us at the Topeka Zoo this evening as a recommendation from AZA's Species Survival Plan.
"He comes from the Akron Zoo and we're very excited to welcome him to his new home. It will be a little bit before guests are able to see this handsome boy but we will provide you with updates!"
