Temporary traffic lights will be installed on the A47 in Mid Norfolk as work is carried out on a collapsed drain.
Traffic has been slow on the busy road since this morning, and motorists have been urged to avoid the area.
A Norfolk police spokesman said: "Traffic lights will be installed on the road and work will be carried out to resolve the problem of the drain. Traffic is still slow. Roadblocks and diversions are in place."
Police were called at 8.41am on Thursday, November 28 to the A47 at Swaffham.
A spokesman said: "There is a collapsed drain in the middle of the Norwich-bound lane, about half a mile from the McDonald's, towards Norwich.
"Highways were called and police have been directing traffic."
Norfolk police tweeted: "#norfolkroads : A47 Eastbound, between Swaffham (McDonald's roundabout) and Necton, Single lane blockage - Traffic is heavy - there will be delays - avoid if possible."
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