The car, a Toyota Tercel, was upright but had a smashed windscreen and appeared to have collided with a sign on the side of the road before coming to rest in the ditch.
Members of the serious crash investigation unit from Christchurch, along with a police photographer, arrived at the scene at around 1am today and were still mapping the scene at 10am.
While details of how the crash occurred were sketchy, skidmarks leaving the road indicated the car may have been travelling north and left the road soon after crossing the Rakaia Bridge.
It was not known whether there were any other occupants in the car at the time of the crash. The deceased woman’s name had not yet been released at time of going to press this morning.