Overhead cables are down over Dereham Road in Watton.
Cars were previously being allowed to pass but high vehicles like HGVs were unable to.
The road has now been shut by police at the junction with Norwich Road and at the traffic lights on the north end of the road.
Traffic is building on the road, with queues on Dereham Road also affecting traffic on Norwich Road and Thetford Road.
It is currently unknown what caused the cables to come down.
For up-to-date information about the county's roads, visit our LIVE Norfolk traffic map.
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