The closure of the A38 in Somerset at Brent Knoll near Burnham on Sea is believed to have been caused by a fire at a nearby small electricity pylon, according to eye-witness reports.
The fire on the electricity pole broke out at around 6.30pm, following a power surge.
Power in the area has been out since the fire broke out and looks likely to remain so for the next two hours.
Engineers from Western Power Distribution are currently trying to rectify the problem.
The road will remain closed until WPD staff locally consider the area safe.
Avon and Somerset Police said the A38 is likely to be closed until 4am tomorrow morning, as the engineers have to deal with what is believed to be a 20,000 volt power line.