The woman was squashed up against the rear window as the front end of the BMW was rapidly submerging into the Waitemata Harbour in Auckland at 3pm on Tuesday.
The officers and a bystander couldn't open the doors so one of the officers tried to smash the window with a baton, but was not successful.
Once it became clear that it was not going to penetrate through the glass another policeman was handed a rock and managed to break the rear window.