Three people, two of them children, were taken to hospital with serious injuries following the collision on Saturday morning.The accident involved a green Land Rover Defender and a white Ford Transit dropside near the St Leonard's junction at Morpeth.
Police said both vehicles were travelling south before the collision took place.
Emergency services, including two air ambulances, attended the scene where the occupants of one vehicle – a 63-year-old woman and two children aged 13 and nine were taken to hospital with serious injuries. The 63-year-old woman remains in a critical condition.
The driver of the Transit was uninjured.
A 28-year-old man was arrested at the scene and has since been released under investigation.
The road was closed northbound and southbound for around four hours.
Officers are now urging anyone who saw what happened, particularly those with dash cam footage, to get in touch.
Anyone with information can contact police by calling on 101 quoting reference 445 15/09/18 or email the investigating officer at: [email protected]