The collision which has left at least two people injured and forced police to close the road in both directions opposite Palmer Park took place at around 3.45pm today.
Among the vehicles involved were a white Ford Transit van and a white BMW which collided near to the junction with Liverpool Road in Newtown, east Reading.
Police are still on the scene and motorists are being warned to expect delays as diversions push traffic away from the crash site.
Reading Buses earlier tweeted there would be delays to a number of its services as a result of the road closures.
A Thames Valley Police spokesman said: "We were called today at 3.47pm to a collision between three vehicles. Two people have sustained injuries but no further details are available at this time."
Ambulance crews are also believed to be on the scene.
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