Emergency services are at the scene. Drivers should expect delays. Traffic cameras show vehicles are not moving. A driver said police cars went by quickly. National Highways said the M4 is closed between junction 17 and 18. Police and traffic officers are there to help.

This live update is now closed.

The M4 in Wiltshire is open again between junction 18 and 17.

There are still some delays of 10 minutes in both directions.