The M4 is closed in both directions between Bath and Chippenham due to a serious crash.
Emergency services, including the air ambulance, are at the scene of the incident between J18 and J17.
The crash happened shortly after 9am and involved multiple cars and a lorry.
Traffic is being diverted off the M4 at J17 but queues are currently stretching halfway to J16 for Swindon West on the westbound carriageway and halfway to J19 for Bristol.
A spokesperson for Wiltshire Police said: "Due to the nature of the collision and the vehicles involved, this closure is likely to remain in place for some time.
"Drivers should avoid the area if possible."
Anyone with information should call 101 and quote log number 93 of Friday 20 October.
Train passengers are also facing disruption this morning as Storm Babet flooded railway lines in Wiltshire.
All lines between Bristol Temple Meads via Bath and Swindon, and Bristol Parkway and Swindon have been closed.