The M4 westbound has been closed between junctions Junction 3 and Junction 4.
An HGV has lost its load onto the carriageway containing a significant amount of seafood and this will take a while to clear up.
Emergency services have been called to the scene of the incident along with recovery and clean up contractors.
Lane Closures are in place and both lanes 2 and 3 are closed.
Highways England advise that the closure could be in place for some time.
More updates to follow.