A three-year-old boy was thrown into a crocodile enclosure at a popular zoo — leaving him in critical condition, police said.

A 30-year-old man was arrested on suspicion of attempted murder after the horrifying incident at the Johnsons Zoo in Old Hurst, England, Thursday.

The suspect, from Norfolk, is not believed not to have known the boy, Cambridgeshire Police said.

The toddler was rushed to a hospital in stable but critical condition.

“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,” Det Insp Verity McCann said told The Sun.

“We do not believe the man arrested and the child are known to each other,” McCann said.

The circumstances of the incident were not immediately clear, police said. The suspect’s name has not yet been released.