Cumbria Police say the A66 will remain closed at Threlkeld "for the foreseeable future".
Diversions are in place.
People travelling from Keswick are asked to travel along St Johns in the Vale.
Those travelling from Penrith, will be turned round at Rheged and are advised to use the M6 routes.
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Trail hunting, where a scent is laid for hounds and the hunt to follow, has been widely practised since the 2005 ban on fox hunting.
Dangerous chemicals stored in a laboratory at the nuclear reprocessing plant have now been detonated by an army bomb disposal team.
Explosives experts were called to the nuclear reprocessing site in Cumbria, to help deal with chemical substances.