Supt Steve Ditchburn said: "We have a significant number of officers actively seeking a suspect."
The force warned business owners and employees that many premises would not be able to open on Tuesday morning.
"Unfortunately due to the extensive cordon, day-to-day business in Clacton town centre has been severely disrupted," said Supt Ditchburn.
"This is necessary to ensure as much early evidence is gathered as possible. We are working as quickly as we can to keep disruption to a minimum."
Police are yet to confirm the identity either of the man killed or the suspect at large.
A mobile police station has been set up in Station Road.
Any witnesses or anyone who has information about the incident is asked to contact detectives or call Crimestoppers.
The B1032 High Street is closed between Station Road and the A133 Carnarvon Road. There are also closures on Rosemary Road, Station Road and Pier Avenue.