A road traffic collision has closed the M4 westbound this afternoon.
Emergency services are attending the scene between junctions 18 and 19 following the incident at around 12.30pm.
Wiltshire 999s understands a caravan has overturned in the crash, leaving debris being strewn across the motorway. 
It’s not yet clear if anyone’s been seriously injured, or how long the road will be closed or partially blocked for.
Motorists are being advised not to join the M4 westbound on the approach to junction 19.
The tailbacks are estimated to be several miles long, hitting Wiltshire’s junction 17 (Chippenham).
Police are also dealing with a collision on the eastbound slip road at junction 18, as earlier reported by Wiltshire 999s.
More follows.
