Christchurch Mayor Bob Parker says the demolition of large buildings in the city centre will slow the process of reconstruction.
An engineering report by Tonkin & Taylor has given the city centre the greenlight for reconstruction with the caveat that stonger foundations may be needed on some sites.
Mr Parker told Morning Report that will raise the cost of rebuilding but demolition is at a critical phase.
He said plans were already in the works to repopulate the city centre with a focus on low rise sustainable buildings.
The Canterbury Earthquake Recovery Authority says it is important to properly co-ordinate the rebuilding of the city centre.
Chief executive Roger Sutton told Morning Report the rebuilding effort will need to be organised so new tenants are not surrounded by buildings in the process of being demolished or rebuilt.
Mr Sutton said he expects most of the cordon around the red zone to be lifted by April.
He did not think that construction will be any more expensive than in Auckland or Wellington.