All lanes have now reopened, but Highways England is warning there are still some slight delays from Junction 6.
An accident on the M4 London-bound at junction 5 has closed two lanes.
Highways England has said emergency services are on the scene in Langley due to a ‘serious’ crash.
Congestion stretches to junction 7 (Slough West) and Highways England has said the incident is causing long delays of at least 30 minutes.
Traffic conditions are expected to return to normal between 1.45pm and 2pm.
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