Gorleston High Street could be closed for 'up to seven days' after a hole appeared in the middle of the road.
The hole appeared without warning shortly before 4pm on Friday, revealing a 1ft x 1ft wide cavity, several feet deep in the centre of the High Street.
Police shut the normally busy strip just before rush hour and Norfolk County Council has put diversions in place.
Anglian Water said the problem was caused by a working sewer which had collapsed and it could take 'up to seven days' to repair as the pipes run in the middle of the main road.
The county council said the problem was first reported to them as a 'depression in the surface' and no immediate action was thought necessary.
But when the cavern appeared, an emergency response team was mobilised.
The sudden closure of the High Street caused considerable confusion on a busy Friday night.
Buses and taxis had to be diverted, while shop workers closing up for the day peered in the hole and pedestrians stopped to take a closer look.
Danny Andrews, who works at the QD Stores directly next to the hole, said: 'There's been a little dent in the road for a while, but it just suddenly appeared.
'It's lucky no one was walking over it at the time. 'I got on the high street radio and the first thing that happened was the butcher coming out of his shop and putting cones around it. The police were here within a couple of minutes and closed the road off.'
Karen Armut, who runs Sunrise Cafe on Gorleston High Street and lives above it, was among the traders keen to know if the road was being closed for the weekend.
'It's caused problems already because it's at rush hour and this road is normally very busy on a Friday night.' she said.
'There has always been a lot of cracks in the road surface. It does makes you worry a bit.'
A similar hole appeared on the A12 near Lowestoft in April.
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