Over 20 tonnes of flour were spilt on the M5 after an articulated lorry carrying it was involved in a crash.
The lorry collided with a car towing a caravan in the early hours of Saturday (5 August) morning. 200 litres of diesel also leaked onto the southbound carriageway.
Jack Tappin, from Highways England, said the articulated lorry "ended on its side in lanes one and two" following the collision, damaging a safety barrier.
One lane remains closed between junctions 14 and 15 in Gloucestershire as a clean-up operation takes place.
Highways England said work to clear the flour, debris and fuel spillage will be completed overnight.
Wiltshire Police said there were no reports of serious injury Sky News reports.