The motorway has been shut because of problems with overhead power lines – as major congestion is expected.
It is currently closed between Burnham-On-Sea (Junction 22) and Bridgwater (Junction 23).
Highways England has dispatched staff to tackle what is said to be an infrastructure repair.
Transport bosses insist they will work to restore normal conditions “as soon as possible”.
But motorists travelling towards the area have been warned to change their route or allow extra time for their journey.
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