Four casualties were caught up in the middle of a police chase when a vehicle refused to stop for inspection.
A woman has died and three people injured.
The victim is understood to have been in one of the two cars that was struck by a vehicle being chased by police in Parklands, Waltham Abbey.
An Essex Police spokesperson said the incident had been referred to the Independent Office for Police Conduct.
The spokesperson said: “We are independently investigating the circumstances of a police pursuit before a fatal road collision in Waltham Abbey last night.
“The car being pursued was then involved in a collision with two other cars in Parklands.
“A woman in one of the cars was sadly pronounced dead at the scene and a number of other people in the vehicles were injured.”
An East of England Ambulance Service spokesperson said: “We were called at 9.59pm yesterday with reports of a collision in Parklands, Waltham Abbey. “Three people were taken to Princess Alexandra Hospital for further treatment.