UPDATE: All lanes have now re-opened and traffic is returning to normal, Highways England said.
The M5 between Weston and Burnham was blocked after a crash this morning which has seen 13 people taken to hospital.
The incident, at around 10.30am, involved multiple vehicles, according to National Highways.
It happened on the southbound carriageway between junctions 21 (Weston) and 22 (Burnham).
Emergency services, including the air ambulance, were sent to the scene.
"Lanes 1 and 2 remain closed for vehicle recovery and scene management," the agency added.
People are being urged to allow extra time for their journeys, with delays around 30 minutes on the approach to the scene.
The South Western Ambulance Service (SWAS) said: “We were called at 10.16am to a road traffic incident on the M5 between junctions 21 and 22.
"We sent an air ambulance, three double-crewed land ambulances, three operations officers, and two hazardous area response teams, and conveyed 13 patients to hospital by land ambulance.”
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