Three people have been taken to hospital and a road has been closed after a crash between two scrambler bikes.
Essex Police was called to Clifton Road, Rochford, at 04:00 GMT to reports of a collision.
Officers remain at the scene and are working with other emergency services to investigate.
Residents have been thanked for their patience by the force as the road is expected to be closed for a number of hours.
Officers appealed for anyone with information or doorbell and dashcam footage to get in touch.