ZSL London Zoo said it is "managing an incident" following reports of an escaped gorilla.
The gorilla is thought to have escaped from its enclosure at the central London zoo, with reports that the public have been locked in.
A zoo spokesman said: "ZSL is managing an incident on ZSL London Zoo."
Footage posted on social media from the zoo shows armed police walking through the zoo's grounds.
Scotland Yard said: "Police were called by security at Regent's Park at 5.17pm to reports of an ongoing incident.
"Officers are there to support ZSL staff."