A section of Somme Parade will be closed for three weeks while contractors install a raised platform to improve pedestrian safety.
The stretch of road between Pitt St and Dublin St will be closed from Monday, November 18 to December 6.
Whanganui District Council's senior roading engineer Brent Holmes said council consulted with the Automobile Association (AA) and the National Road Carriers Association on the raised platform, which is part of the Whanganui urban transportation strategy.
"Having this raised platform in place will enhance the experience of pedestrians and people who are choosing active travel options along the riverfront," Holmes said.
"It will also provide a safer and more visible crossing point for those using mobility scooters or wheeling strollers. However, users need to remember that vehicles still have right of way at raised platforms."
Detours will be available via Pitt St or Dublin St during the closure.
Contractors will use stop-go signs during peak hours between 3pm and 6pm, Monday to Friday.
Delays are likely as motorists are advised to use Glasgow St, Bell St, Whanganui City Bridge or Cobham Bridge as alternative routes.
Holmes said council would appreciate everyone's patience while work is under way.
"The work was scheduled for this time to ensure it is completed before a number of large community events, including the Whanganui 3 Bridges Marathon."