The A11 has re-opened in both directions between Snetterton and the A1075 following an earlier closure, but delays remain.
The closure was sparked by reports of an incident involving a firearm at a building in Larling at 4.50pm.
Officers said they closed the A11 for the safety of the public while they dealt with the call.
A man in his 40s was arrested on suspicion of assault and threats to kill.
He will be taken to the Wymondham Police Investigation Centre where he will be questioned today
There was no access to the A11 between Snetterton and the A1075 and diversions were put in place.
Drivers were also held up the A11 this afternoon and this evening because of snow.
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