A woman died this morning following a collision with a tipper truck and police are urging drivers to be patient with the diversions as they investigate.
It happened just before 8am near Barnstaple at Brynsworthy Bickington.
A force spokesman said: "Tragically, a 59-year-old local woman died following the collision. Her next of kin have been informed.
"Closures were put in place in the area including on the A39 including at Westleigh, at Roundswell Roundabout and the Instow turn off to allow emergency services to work at the scene.
"Closures are expected to remain in place until the middle of the afternoon at the earliest as scene investigation work continues; road users are advised to avoid the area."
Inspector Si Jenkinson Tweeted: "Please be patient if you are affected by the road closure and diversions.
"Our officers are conducting their enquiries as effectively as they can."