The M5 link road was also shut south to M4’s junction 20 west, National Highways said.
Traffic was being turned around in sections under the supervision of Traffic Officers and the police, National Highways said.
One motorist said on social media their family had been trapped in the road closure since 7pm without food, water or toilet facilities.
National Highways said turning vehicles around ‘is a complex and time consuming operation due to the volume of traffic and location.’.
Avon and Somerset Police said: ‘Enquiries are underway to identify the deceased and notify next of kin, while an investigation to establish how the person came to be on the motorway continues.’.
