A small aircraft has crashed into a reservoir, police said.
Essex Police was called shortly after 14:00 GMT on Sunday to reports of the aircraft entering the water at Hanningfield Reservoir, near Chelmsford.
On Monday, the force said its officers remained on the scene of a serious incident and were working with several organisations.
Ch Supt Waheed Khan said: “We are still in the early stages of our investigation and are working closely with the Air Accident Investigation Branch to establish what has happened.”