Prime Minister John Key also says thousands of homes will have to be demolished because of all the damage. he says some of the land has liquefied and is not sturdy enough to rebuild.
The magnitude 6.3 temblor that hit Feb. 22 shattered homes, heritage buildings and office blocks, and caused 166 confirmed deaths. Officials expect the toll to rise to more than 200 as rescuers continue to search for bodies in the rubble.
Rescuers saved 70 people in the first 26 hours after the quake struck just before 1 p.m. on Feb. 22, but no one has been found alive since.
Work crews are still clearing rubble from the earthquake, which badly hit the downtown area.
The earthquake cut water and power services across the city. Almost all electricity supplies have been restored, but residents in the city are being told to boil tap water because of the risk of contamination.
Officials say about one-fifth of Christchurch's population of 350,000 have left the city temporarily as a result of the quake.
The Associated Press contributed to this story.