Traffic is being held on both the eastbound and westbound carriages from Junction 15 to 16 – around Swindon. National Highways said the closure is expected to last “throughout the morning”.
Traffic monitors suggest the road was initially closed around 5.50am this morning. The incident was first reported by National Highways just after 6am.
It said the motorway had been closed “to allow Wiltshire Police to respond to an ongoing incident”.
It added: “The road is expected to remain closed throughout the morning.
“There are currently slight delays approaching the closure in either direction. If this closure impacts on your planned route, please allow extra journey time.
“Plan ahead, you may wish to re-route or even delay your journey.”
Wiltshire Police noted that “Croft Road in Wroughton has also been closed as a result of this morning’s incident.”
They advised: “Please avoid this area if you can.”
More to follow…