It is believed that two men - each riding a motorbike - were travelling along the southbound carriageway when, for reasons to be established, one of the riders collided with a Nissan Juke car.
Officers say both riders fell off their bikes and one suffered serious but non-life threatening injuries to his leg and remains in hospital.
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The second rider had already left the scene before emergency services arrived and attempts are ongoing to trace him.
Following the incident, the A189 was closed for several hours yesterday as the Northumberland Fire and Rescue service, North East Ambulance Service, Northumbria Police and the Air Ambulance attended.
As part of their enquiries, officers have now released an image of a man who they would like to trace.
The man is believed to have been in the area and could have information to assist the investigation.
Sergeant Dave Roberts, of Northumbria Police’s Motor Patrols Department, said: “This is a serious collision that resulted in the road being closed for a number of hours.
“We want to build a clearer picture as to the full circumstances surrounding the collision, and as a result, we want to speak to the man pictured who was seen walking down the carriageway near to where the collision took place.
“I would ask that the man, or anyone who recognises him, to get in touch as soon as possible to assist our ongoing investigation.
“We also want to hear from anybody who witnessed the collision, or who was driving on the Spine Road at that time and saw two motorcyclists. Please check any dashcam footage and get in touch if you can support our enquiries.”
The driver of the car remained at the scene and is assisting the ongoing investigation.
Anyone with information is asked to contact police via the ‘Tell Us Something’ page of our website or by calling 101 quoting log NP-20220803-0948. Alternatively, you can email [email protected]