The carriageway is now fully reopened and delays are beginning to clear.
Motorists heading towards London are facing severe delays after a serious accident between junctions 11 and 10 on the M4 eastbound.
The carriageway is closed and diversions are in place, with Highways England warning of one-hour delays.
The M4 is open beyond junction 10, but motorists heading into Maidenhead and Slough from the Reading area are likely to be severely delayed.
Normal traffic conditions are not expected until at least 1pm.
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