Route 320 buses will be diverting from 12pm to 4pm due to road closures in place for a planned Police Operation protest march.
Services will be split into two routes between Central and Green Square, and between Wynyard and Gore Hill.
Services to the city from Zetland will end trips at Rawson Place, Central, return services will pick up from Lee St at Central.
Services to the city from Gore Hill will end trips at Wynyard York St, return services will pick up from York St.