Diversions were put in place on Wednesday for the start of major gas main works in King’s Lynn.
The Saturday Market Place is now closed to traffic as a result of the work, which started this week.
The project, which involves replacing iron mains with plastic pipes, is expected to last until Friday, March 28.
National Grid has said the work is essential to ensure it could continue to provide reliable gas supplies for the local community into the future.
Anyone who has any queries about the work should call 0800 096 5678.
The diversion is routing traffic down College Lane and back through South Quay. There are traffic lights near King Staithe Square at the top of Purfleet Street and at the Baker Lane car park.