London Zoo was put in lockdown for around two hours on Thursday evening (local time) after a gorilla escaped from its enclosure.
There are reports the gorilla was throwing himself at the window of his enclosure before the escape, but it's not yet known how he got free.
Visitors to the zoo were kept inside buildings at the zoo, including a cafe and the butterfly enclosure, while keepers searched for the animal.
Police and an air support unit helped to locate the gorilla, who was was successfully tranquilised and recaptured.
The incident comes only months after Harambe, a gorilla at Cincinatti Zoo, was shot and killed after grabbing a child who had fallen into its enclosure.