Vehicle fire closes motorway after collision
In an update at 21:36 GMT,, external[1] National Highways said the M4 westbound was closed between junctions 11 and 12, as oil and fuel from the collision was "across all lanes".
It said contractors were attempting to clean the road surface and "a decision to resurface or not will be made soon".
A statement from National Highways said "both vehicles are completely burnt out so recovery will be protracted".
At 20:00 BBC Radio Berkshire reporter Patrick O Hagan said he had been stuck in the traffic since 17:45.
He explained: "Every so often a police car comes up alongside on the inside lane heading up to whatever's going on.
A lot of frustration here, who knows when we'll be released."
Thames Valley Police and Royal Berkshire Fire and Rescue Service have been contacted for comment.