"The impact caused the Nissan to drift sideways and onto the side of the road. The car tipped over, but fortunately landed back on its wheels without rolling over," said Mr Moore.
The woman's car came to rest about 300 metres north of McLeans Island Road, opposite The Press printing plant.
The four-wheel-drive vehicle left the scene without slowing or stopping.
It may have turned right onto McLeans Island Road.
"The driver was not hurt but was very shaken by the incident, which appeared to be totally unprovoked," said Mr Moore.
"The only thing the driver has done was to slow down - correctly - for road works.
"This incident could easily have resulted in serious injuries to the victim and to other road users."
Police believe there were two occupants in the four-wheel-drive.
The driver is described as a clean-shaven Caucasian in his 20s, and the passenger is described as a Caucasian woman of similar age, with long blond hair.
Investigators have spoken to the driver of the Nissan and to another witness, but are appealing for additional information.
"We know there were other witnesses, and we would like to hear from them as soon as possible," Mr Moore said.
"We're also seeking help from anyone who can help identify the white four-wheel-drive vehicle, or its occupants."
Anyone with information is asked to contact Senior Constable John Moore on (03) 3637336 or Christchurch police on (03) 3637400.
Alternatively, information can be provided anonymously by contacting Crimestoppers on 0800 555 111.
