A woman has died and a three people have been injured in a horror crash following a police pursuit.
The victim is understood to have been in one of two cars that was struck by a vehicle being chased by police in Parklands, Waltham Abbey.
The crash is being investigated after the car had failed to stop for officers on the M25 shortly before 10pm on Thursday.
Witness Margaret Parrot told BBC Essex she heard a man who was in one of the vehicles shouting to an injured woman "don't go".
"It's terribly tragic, very, very sad," she added.
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An Essex Police spokesperson said the incident had been referred to the Independent Office for Police Conduct.
The added: "It followed a police pursuit involving one of the cars, which officers from the Bedfordshire, Cambridgeshire and Hertfordshire road policing unit had attempted to stop on the M25."
An IOPC spokesperson said: "We are independently investigating the circumstances of a police pursuit before a fatal road collision in Waltham Abbey last night.
"We understand that the pursuit took place after a car failed to stop for officers from the Bedfordshire, Cambridgeshire and Hertfordshire Police roads policing unit at around 9.55pm.
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"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.
"After we were notified by Hertfordshire Police we sent investigators to the scene and to the police post incident procedure to begin gathering evidence."
An East of England Ambulance Service spokesperson said: "We were called at 9.59pm yesterday with reports of a collision in Parklands, Waltham Abbey.
"We sent two ambulances, a rapid response vehicle and an ambulance officer.
"Three people were taken to Princess Alexandra Hospital for further treatment.
"Sadly despite our best efforts one patient died at the scene."
Witnesses and people with dash-cam footage are asked to call the Serious Collision Investigation Unit on 101.
