Police are searching for a white tray-back utility with South Australian number plates after the four-wheel-drive rammed a stationary police car in Williams last night.
A female officer from Narrogin police was treated for minor injuries following the incident on Albany Highway about 8.25pm.
The Toyota Hilux police vehicle was pushed back almost 1m by the impact of the ute reversing into it.
The offending vehicle then took off at speed in a southern direction along Albany Highway.
The female officer has returned to duty.