A driver was knocked unconscious in a crash involving another car that failed to stop.
Police were called to Queenborough Lane, Rayne, near the A120, at about 10pm on Sunday.
The blue Ford Fiesta was on its side in a ditch and the woman driver, who had been unconscious when paramedics arrived, was taken to Broomfield Hospital, Chelmsford.
There are no details about the other car which was travelling from Rayne towards the A130.
Any witnesses, or the driver involved, should contact the investigating officer PC Allan Discombe at Stanway road policing unit on 101.