The M5 southbound is closed at J27 A361 (Tiverton) because a lorry has overturned. Lane three is also closed on the northbound carriageway.
The 23-year-old driver was injured and he was taken to hospital, but his injuries are not believed to be life-threatening or life-changing.
Traffic is diverting up the exit slip road and back down the entry slip road.
Diesel was flowing from the lorry, the fuel spill makes the clear up operation more difficult.
Police say the road is "likely to remain closed until 18:00 tonight" but that highways engineers were "working hard to reduce this".