A police officer suffered minor injuries after a white 4x4 collided with his car in Runcorn.
Cheshire Constabulary are now trying to trace the vehicle's driver, who failed to stop at the scene.
The collision between the 4x4 and police car happened at 12.18am yesterday at the junction of Halton Road and Bridge Street.
A Cheshire police spokesman said paramedics treated the officer at the scene.
Enquiries are ongoing and investigators want to hear from anyone with any information that might help the investigation.
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A 35-year-old Runcorn man was arrested on suspicion of failing to stop following a collision, and drink driving.
He has since been released under investigation.
PC Paul Cullen said: "Thankfully the officer involved in the collision sustained only minor injuries.
"However, the outcome could have been far worse.
"Enquiries in relation to the incident are ongoing and as part of the investigation I am keen to hear from anyone who witnessed the collision or has any other information which may help our investigation.
"I am particularly keen to speak to the driver of a small hatchback car which was seen driving past the police car at the time of the incident.
"I also urge any drivers with dashcam footage who were driving on Halton Road or Bridge Street around the time of the incident to get in touch."
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