There are delays of up to 20 minutes on the A303 in in both directions between A30 (Upottery) and A358 / B3168 Station Road (Southfields Roundabout, Ilminster).
The road is closed due to a serious accident. Two vehicles were involved.
Air ambulance attended the scene. One person was airlifted to Frenchay Hospital in Bristol. Police say the person is seriously injured.
More top news
Your latest West Country weather forecast with Bob Crampton.
A coroner has ruled a "series of failures" contributed to the death of a newborn.
Cornish charity ShelterBox has flown volunteers to the Turkey-Syria border to help deal with growing number of refugees there.