The A30 is likely to be closed for "many hours" after a man suffered serious injuries in a crash.
The key Devon route is closed in both directions between Daisymount Cross and Honiton, with miles of queues building. Cullompton services on the M5 have also been closed due to volume of traffic
Police were called to the A30 at 12.20pm on Friday 9 July to reports of a road traffic collision.
A spokesperson for Devon and Cornwall Police said the road "may be closed for many hours".
"A man has sustained serious injuries and emergency services are in attendance at the scene," the spokesperson added.
"The road is currently closed in both directions which is likely to cause significant traffic disruption. The incident is ongoing."
Traffic is being turned around and a full closure is in place at Daisymount Cross.
Diversion routes in place
Westbound motorists are being diverted:
At Honiton exit the A30 and travel south on the A375 vis Sidbury to Sidford
At Sidford turn right and travel west on the A3052
At Half Way House turn right onto the B3180 travelling north
Re-join the A30 at Daisymount
Eastbound motorists should follow the above route in reverse to bypass the incident.