The M5 Southbound between junctions 25 and 26 (Taunton) is expected to stay closed until at least 11am.
It's following a crash in which a man in his 20s died. Another two people have been taken to Musgrove Park hospital in Taunton in a life threatening condition. All were travelling in the same car.
Police are appealing for witnesses to the crash.
Motorists are being advised to take alternative routes.
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