The northbound carriageway of the motorway is fully closed between J46 (Flaxby) and J48 (Boroughbridge) near Knaresborough in North Yorkshire.
It follows two collisions on the route during the early hours of this morning, one of which left a lorry driver seriously injured.
Highways England said the road was likely to remain closed throughout the morning peak and delays should be expected as vehicle recovery work continued.
Firefighters and police were first called out to the motorway between junction 47 (Allerton Park Interchange) and junction 48 at 2.15am.
North Yorkshire Fire Service said crews from Ripon, Harrogate and Knaresborough responded to a collision involving a Mercedes van and a Ford van.
A spokesman said the driver of the Ford had suffered minor injuries, while the Mercedes driver had fled the scene.
Crews helped police make the vehicles safe and searched the immediate area.
Just after 2.40am, a second collision involving two articulated lorries was reported on the same stretch of motorway.
Crews from Ripon, Knaresborough, Boroughbridge and Harrogate were among the first at scene, administering first aid until paramedics arrived and providing scene lighting for police.
The spokesman said one male lorry driver had been ejected from the vehicle and was taken to hospital with serious injuries.
The second male driver received a precautionary check up from paramedics on scene, he added.
What route should drivers on the A1(M) northbound follow?
A diversion route for northbound traffic arriving at J47 is in operation.
Road users should follow the 'solid black square' diversion symbol.
Exit the A1(M) at J47 and take the second exit onto the A59.
At the next junction take the A168 and continue along this road to the junction with the A6055.
Continue A6055 for approximately 200 metres to re-join the A1(M) at J48.
Northbound traffic from J46 is advised to follow the 'solid black square' diversion symbol, taking the B6146 west and then the A168 northbound which takes traffic to J47 to follow the above route.
Road users are advised to allow extra time for their journey.