The southbound carriageway has been closed after the incident and a diversion route has been put in place.
Durham Police first received reports of a single vehicle crash where a car had left the road and hit a tree at 4.57am.
Police attended the scene and while they were there a second vehicle “caused a collision” at the scene.
One man has been taken to hospital with “serious injuries”.
A Durham Police spokesperson said: “The southbound carriageway of the A19 near Castle Eden is currently closed following two road traffic collisions this morning.
“One man has been taken to hospital with serious injuries.
“Drivers are asked to avoid the area and find an alternative route while the cars are recovered.
“We will update you as soon as the road is reopen.”
A National Highways spokesperson said: “The road has been closed following a single vehicle collision where a vehicle has left the carriageway and struck a tree. Durham Constabulary received reports at 04.57 of this initial collision.
“Durham Constabulary attended the scene and whilst in attendance a secondary vehicle has caused a collision at scene.
“Durham Constabulary lead the response to this incident and have reported that several lamp columns have been damaged at scene which will require assessment and repair prior to reopening the carriageway.
“There is currently no estimate for when the road will reopen, but it is likely to remain closed for several hours.”
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Here is the full diversion route:
- Exit the southbound A19 and follow the exit slip road until it meets the A181.
- Turn left onto the A181, which leads straight onto the B1281.
- Head east for 800 meters, then turn left in Castle Eden continuing on the B1281 for 2.7 miles.
- At the junction in Blackhall Colliery, turn right (south) on the A1086 for 2.6 miles.
- Take the second exit on the roundabout continuing on the A1086 south-eastwards for a further 0.7 miles.
- Take the third exit at the roundabout junction with the A179.
- Take the A179 westbound and travel for 3.2 miles in a north-westerly direction, over 2 roundabouts.
- At the A179/A19 junction, take the entry slip road to rejoin the southbound A19.