Northumbria Police officers received a report that a silver Mazda 2 had left the road in Hexham and collided with a tree near the Broomhaugh roundabout on the A68.
The incident happened at 12.20pm on Wednesday, September 18.
An 89-year-old woman, the driver of the Mazda and the only occupant of the vehicle, was rushed to hospital after suffering serious injuries in the collision.
No other vehicles were believed to be involved in the collision but enquiries into the circumstances around the collision are ongoing.
Police have now launched an appeal for any witnesses to the incident to get in touch with officers.
Sergeant Matt Sykes said: “This collision has happened on the northbound carriageway and we believe the Mazda was the only vehicle involved.
“We are trying to establish how and why the vehicle left the road and need any witnesses to the collision to get in touch.
“We also need to speak to anyone who may have seen the Mazda in the minutes before the collision as it travelled northbound on the A68.
“Our investigation team are particularly keen to speak to anyone who may have dashboard footage from the time in question.”
The road was closed for more than four hours before being re-opened at 4.30pm on Wednesday afternoon.
Anyone with information is encouraged to contact Northumbria Police on 101 quoting log 423 18/09/19 or email the investigating officer on [email protected]