Two police officers and a taxi driver have been taken to hospital after a crash.
One of the men, a special constable, is in a critical but stable condition following the collision in Basildon, Essex.
The police car was travelling to an emergency and had its siren and flashing lights on.
The crash happened just before midnight in Broadmayne and involved an Essex Police Ford Focus and a white and orange London-style taxi.
A police spokesman said: "The police car turned on its side and the fire service was required to release the officers.
"The driver, a constable aged in his early 30s, was taken to Basildon Hospital.
"The passenger, a special constable, was taken to Basildon Hospital but then transferred to the Royal London Hospital where he is described as being critical but stable.
"The taxi driver, a 26-year-old man, was also treated at Basildon Hospital."
The road was closed overnight.