The 85-year-old was on a traffic-light-controlled pedestrian crossing near the intersection with Law St, when the incident occurred.
It appeared the woman was crossing from the northern side of the road, near the Blind Foundation, when she was hit about 10.30am.
The serious crash unit is investigating.
It is unclear what led to the incident.
The road was closed while investigators carried out a scene examination.
At least four police patrol units and two ambulances attended the incident.
''The elderly woman in her 80s is still in a serious condition and is likely to be flown to Christchurch Hospital for further medical assessment,'' a police spokeswoman said yesterday afternoon.
A St John spokesman said the woman was taken to Dunedin Hospital's emergency department by ambulance. She was later admitted to the high dependency unit in a serious condition.
It is unclear if the woman was coming from the Blind Foundation.
