Paramedics from the East Of England Ambulance Service were called to a lay-by on the A12 on Thursday morning.
Upon arriving at the scene, they found a patient who required urgent medical attention before rushing the casualty to Queen’s Hospital, in Romford, by a road ambulance.
A spokesman for the East Of England Ambulance Service said: “One ambulance, one rapid response vehicle, one ambulance officer vehicle and Essex and Herts Air Ambulance were called to a lay-by on the A12 this morning following reports of a medical emergency.
“One patient was transported in a serious condition to Queen’s Hospital Romford by road ambulance.”
Essex Police were also called to the scene after receiving a request from the ambulance service for assistance at the incident.
The force’s officers subsequently closed the road and stopped traffic in both directions between Junction 16 and Junction 17.
It led to seven miles worth of congestion on the A12’s southbound carriageway and three miles of congestion on the A12’s northbound carriageway.
The road closure has now been lifted and traffic has resumed.
The individual’s current state is unknown.