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.”
He urged anyone with information, CCTV, dash cam or other footage to get in touch.
The public has been asked to avoid the area.
A spokesperson for the Essex Wildlife Trust, which manages a nature reserve at the reservoir, confirmed its visitor centre would remain closed on Monday.
