Part of the M4 near Bristol was closed today after liquid propane gas (LPG) leaked on to the carriageway following a collision, the Highways Agency said.
A light goods vehicle carrying cylinders of LPG is believed to have collided with a van.
The motorway was closed in both directions between junctions 19, for the M32 and Bristol, and 20, for the M5 north and south, and was likely to remain so until this afternoon.
The M5 north to M4 east slip road and the M5 south slip road to M4 east were also closed.
An Avon and Somerset Police spokesman said no one is thought to have been injured.