Work to repair a collapsed sewer near the world famous Eastgate Clock will start on Tuesday (July 28).
Part of Eastgate Street will be closed to traffic for a week for the emergency repairs.
The closure will affect the city centre street between St Werburgh Street and St John Street.
Access for pedestrians will be maintained.
Up to 10.30am, delivery vehicles turning right onto Eastgate Street will not be affected.
Daniel Contractors Ltd will undertake the work on behalf of Welsh Water.
They will be contacting each business, hotel and church within the closed area and in St John Street to discuss alternative access arrangements while the emergency work is carried out.
The remainder of the premises will be served by access along St Werburgh Street and Northgate Street with the one way at the barrier at the Town Hall lifted for the duration of the works.
Martin Williams from Welsh Water said: "We will ensure this work is carried out as quickly as possible, with minimum disruption to the public.
"There will be no impact on water and sewage services to residents or businesses in the area while it takes place.
"We carried out a CCTV survey to determine the location of the collapse and are currently investigating to establish the cause.
"We would like to apologise for any inconvenience caused."
Planning the work was made easier with the help of Subsurface Geotechnical, a geophysics company which was carrying out a survey for Cheshire West and Chester Council along St Werburgh Street.
The company, using sophisticated ground penetrating radar equipment, was able to give an approximation of the void.
The information gathered by the firm is being used to plan how the work will be carried out in order to minimise the length of time the repairs will need.
Cheshire West and Chester Council, which is the highway authority, is working closely with Welsh Water.
Cllr Neil Ritchie, executive member for environment, said: "We will be working with other agencies to protect the arch and the Eastgate Clock.
"It was fortunate that we had access to geophysical information which has been an invaluable planning tool."