Three children and five adults have been seriously injured in a collision involving a police car and two other vehicles near Southend-on-Sea.
The marked police car, carrying two officers, was responding to an emergency and using its siren and lights when the crash happened, Essex Police said.
A woman in her 70s driving a Fiat and a BMW carrying a man, woman and three boys were involved in the incident on the A127 shortly before 4pm.
The Fiat driver had to be freed by the fire service after her vehicle left the road near the junction with Daws Heath Road and ended up on a verge, police said.
The occupants of the black BMW - including the three boys aged five, seven and 11 from Basildon - were not trapped.
All the people involved were taken to Southend General Hospital with serious injuries.
The collision is being investigated by the serious collision investigation unit (SCIU), and the force's professional standards department has been made aware, police said.
The two injured officers are both men, one in his 40s and the other in his 20s, and are based at Boreham.
The crash forced the closure of the A127 near to where it had been shut because of flooding.
Anyone with information is asked to call Essex Police or email firstname.lastname@example.org.