At least one person may still be inside the 17-storey Forsyth Barr building where American search and rescue teams are working.
After the stairway of the 17-storey building collapsed in Tuesday's quake, some people abseiled to safety while others were rescued by crane.
On Saturday, Christchurch Mayor Bob Parker said crews working at the building were not conducting a rescue mission but carrying out an inspection.
However, the taskforce leader of urban search and rescue, Paul Burns, says rescue workers learned several days ago that at least one person in the building is unaccounted for and there may be more.
He says the American teams are doing engineering work as they prepare to search every part of the building.