The A140 is due to partially re-open at Long Stratton after a shattered manhole cover led to a five-hour closure.
Fire crews from Long Stratton and Carrow were called at 4.05pm and are still on the scene close to the Stratton Motor Company.
There were reports of a loud bang and a blast that blew open a manhole cover. Police said the manhole cover 'shattered without warning close to the road'.
A spokesman from UK Power Networks said engineers arrived on the scene at 5pm and investigated a fault on the electricity network.
A statement issued shortly before 9pm said: 'UK Power Networks engineers continue to work in the Flowerpot Lane area of Long Stratton to carry out emergency repairs on a piece of underground equipment.
'Power supplies have been restored to the area and traffic management is being established to allow the partial re-opening of the A140.
'We apologise for any inconvenience caused.'
James Betts, sale manager at Stratton Motor Company, where a cordon is in place, said he heard a loud bang.
The manhole is at the southern end of Long Stratton next to the forecourt of the Shell petrol station.
Several houses close to the scene were evacuated.
Roger Ranson, who works next to the Lotus garage close to the petrol station, said: 'Just after 4pm lots of emergency vehicles arrived and cordoned off the road.
'I was told a policeman saw the manhole cover rise to the height of a dustbin. At the time it was quite alarming near a filling station and those expensive Lotus cars.
'It's quite eerie - normally at this time of day the road is quite busy.'
Diversions were in place and motorists were advised to find alternative routes.
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