A "HUGE" combine harvester has completely blocked the A34 northbound, causing heavy traffic.
Part of the machinery detached from the vehicle as it was in transit on the busy dual carriageway.
The precise scene of the incident is between Chilton and Chieveley, near the M4.
Thames Valley Police are carrying out a removal operation and have confirmed that no one has been injured.
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An eyewitness reported: "Traffic southbound is very slow with drivers looking at the incident."
This is evident in the updates from the AA, which has recorded delays of 36 minutes northbound with an average speed of 10 mph, and six minutes southbound.
The National Highways also warned of delays, saying: "The #A34 in #Berkshire is CLOSED northbound between the #M4 (#Chieveley) & the #A4185 (#Chilton) due to a combine harvester which has fallen from the back of a tractor and is blocking the road.
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