A wildlife advocacy group has warned that the escape of a silverback gorilla from the London Zoo that ended without injuries to visitors or the animal could have ended very differently.

Chris Draper of the Born Free Foundation said Friday the group is "relieved" no people or animals were hurt but said it was a reminder of the risks of keeping dangerous wild animals in captivity.

Male gorilla Kumbuka escaped from his enclosure Thursday evening, leading some zoo visitors to be locked inside of buildings until the animal was subdued by a tranquilizer dart.

Armed police descended on the zoo. Officials said the public was not in danger and the gorilla was back in his enclosure within an hour.

An investigation into the escape is underway.