An operation at the Forsythe Barr building in the central city is not a rescue mission, says Christchurch Mayor Bob Parker.
Several people have been lowered on to the building by helicopter and were observed peering into the lift shaft.
But Mr Parker says the building's stairwells have collapsed and it was the only way to get on to the building.
He says it is simply a building inspection.
The PricewaterhouseCoopers building will be inspected in the same way.