The work is being done now because an attempt to upgrade the street in May could not be completed because of heavy rain.
Waitaki District Council roading manager Michael Voss said the upgrade involved drainage improvements, expected to take up the first week, followed by road reconstruction for about a week.
The upgraded road will have a lifespan of 30 years with maintenance taking place every 10 to 12 years.
For the work to be carried out, Harbour St is temporarily closed to vehicular traffic but footpaths will remain open, as will the businesses along the street.
''We have worked very closely with businesses to get the best timing for the roadworks which must be done,'' he said.
Waitaki Mayor Gary Kircher said the council appreciated the co-operation of Harbour St business owners to ensure the work was carried out as efficiently as possible, with as little inconvenience as possible.
Harbour Street Bakery owner Ed Balsink said while the road closure was an inconvenience, the work was necessary to make the street more attractive.
To encourage foot traffic down Harbour St while the works were carried out, Mr Balsink was offering specials on bread and pies on Tuesdays and Thursdays.
The Oamaru Whitestone Civic Trust was yesterday organising a sign which would list the businesses in the precinct, emphasising that the street remained open to foot traffic during the upgrade.
