A man has been arrested on suspicion of attempted murder after a three-year-old boy was left with critical injuries after ending up in a crocodile enclosure.
Cambridgeshire Police said it was called to Johnsons Zoo in Old Hurst, near Huntingdon, at 13:24 BST.
The boy was taken to Addenbrooke's Hospital with serious injuries and is in a critical but stable condition, the force said.
A 30-year-old man from Norfolk has been arrested on suspicion of attempted murder and officers added that they do not believe the man and child were known to each other.
The force said it was investigating whether the child was attacked by the animals.
Det Insp Verity McCann, from Cambridgeshire Police, said: "At this stage we are speaking to people who were at the zoo at the time of this distressing incident to understand more about the circumstances.
"We do not believe the man arrested and the child are known to each other. Officers are supporting the boy's family at hospital, and our thoughts remain with them."
Huntingdon MP Ben Obese-Jecty wrote on social media that his "thoughts were with the young victim and his family during a hugely traumatic and difficult time" and urged people to "refrain from speculation online".
He said he was "liaising with senior officers at Gold Command who are treating this as a critical incident".
Darryl Preston, Cambridgeshire and Peterborough's police and crime commissioner, said he had been briefed by chief constable Simon Megicks from the police force.
"My thoughts go out to the family of the little boy involved in this truly horrific incident," he said.
"I can only begin to imagine the trauma those involved are going through," he added.
Johnsons Zoo's website said it "houses over 100 fascinating animals" including crocodiles, African lions and a Bengal tiger.
A spokesperson for the East of England Ambulance Service said an ambulance, a rapid response vehicle, an ambulance officer vehicle and Magpas Air Ambulance attended the scene.
"A child was transported by road to hospital for further care," they added.
A Magpas Air Ambulance spokesperson said a critical care team attended the incident at 13:42 and "treated one patient at the scene before taking them to hospital".
