Essex Police is increasing patrols across the county following the terror attacks in London.
In a separate statement the force said the car used to hit pedestrians on Westminster bridge was not registered in Essex.
The statement added: "Essex Police are not looking for any vehicle in connection with the incident and there is no suggestion that any Essex-registered vehicle is involved."
However, the force is putting extra regular and armed officers on the streets as a precaution.
Acting Assistant Chief Constable Andy Prophet said: "This has been declared a terrorist incident in London and is being investigated by the Metropolitan Police Counter Terrorism Command.
"In Essex tonight, and until further notice, there will be increased visible police patrol including additional armed officers and other specialist resources.
"I urge the public to be alert but not alarmed. Police forces and our partners are doing everything we can to help protect the security of our citizens, public institutions, critical national infrastructure, and businesses and places.
"This is a time for communities in Essex to remain resilient, compassionate and supportive of each other. Should anyone have any concerns or see anything suspicious I would urge them to report it immediately by calling 101 or 999 in an emergency."
Acting Assistant Chief Constable Andy Prophet also paid tribute to those who died.
He said: "On behalf of Essex Police I want to offer the thoughts and prayers of the entire force to members of the public killed, injured or affected by the incident in London today. We of course also join our colleagues in the Metropolitan Police Service in grief for the loss of a serving officer."