THE M4 is currently closed eastbound between junctions 11 for Reading and 12 for Theale after a cement mixer overturned.
Two lanes are also closed westbound and police are advising motorists to avoid the area while the vehicle is recovered.
The driver of the cement mixer has reportedly been taken to the Royal Berkshire Hospital.
A spokesperson for Thames Valley Police, James Williams said another car, a Ford Mondeo is believed to be involved and has now been recovered.
The Highways Agency says the road is not expected to fully reopen until after the evening rush hour at the earliest.
A diversion is in place via the A4, A4155 and A33 to rejoin the M4 at junction 11. Long distance traffic approaching junction 13 eastbound is encouraged to use the A34 southbound, A303 eastbound and M3 eastbound.
Drivers planning to use this section of the M4 are advised to plan their journeys and allow extra time to reach their destinations.
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