A three-year-old boy is in a critical condition after being injured in a crocodile enclosure at a popular British zoo west of London.

In a statement, Cambridgeshire Police said they had arrested a 30-year-old man on suspicion of attempted murder following the incident.

They were called to Johnson’s of Old Hurst, otherwise known as Johnson’s Zoo, shortly after 1pm local time on Thursday (10pm AEST), after reports that the boy had ended up in the attraction’s crocodile enclosure.

He suffered serious injuries and is in a critical but stable 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,” Cambridgeshire Constabulary Detective Inspector Verity McCann said.

“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.”

The force said specially-trained officers were supporting the boy’s family at Addenbrooke’s Hospital.

According to the attraction’s website, Johnson’s Zoo is home to crocodiles, lions, tigers and sloth bears.

The area’s local MP, Ben Obese-Jecty, wrote on X that he was aware of the incident.

“My thoughts are with the young victim and his family during a hugely traumatic and difficult time,” he wrote.

“This is now a live criminal investigation and I would ask people to refrain from speculation online. The police will provide an update with further information in due course.”