The animals, which can be grow to around 5ft tall and have a top speed of 50mph, have been spotted near Maple Cross, Hertfordshire with police warning they have been spotted attacking dogs.
Similar to an ostrich but smaller, the animals are believed to be wild.
PC Christian Gottmann, from the Rickmansworth and District Safer Neighbourhood Team, said: “These birds are certainly an unusual sight on the streets of Three Rivers.
“We want to reassure the public that we are working in partnership with Three Rivers District Council, Highways and our Rural Operational Support Team to come up with a plan to capture and rehome the birds to a suitable animal reserve.Advertisement
“If you think you may be able to help with this, please get in touch with us. In the meantime, we would advise the public not to approach these animals as they are very fast, much like their larger counterparts, and can be aggressive if cornered.