Police are carrying out aerial searches of a park following a number of sightings of a big black cat.
The animal was reported to be the size of a puma
Essex Police said people had reported seeing the animal in Weald Country Park, in Brentwood, and described it as being the size of a puma.
A police spokeswoman urged people to report any sightings and not to approach the animal. Pet owners were asked to keep their animals inside.
Wildlife parks in the area are being contacted to check their animals.
The spokeswoman said there was also an isolated report that a deer had been killed by the cat, which officers were investigating on Tuesday.