The Christchurch City Council suspects some people with homes in the Port Hills and Lyttelton are still living in them despite being issued notices prohibiting entry for safety reasons.
The council says notices under the Building Act have been issued to about 500 homes as they are at risk from rockfall and land movement caused by the recent earthquakes.
The general manager of the council's Regulation and Democracy Services says if enforcement is required, those property owners will be served with a notice to fix - effectively an immediate order to evacuate.
Peter Mitchell says the council is investigating reports of lights on late at night and smoke coming from some chimneys.
However, some former residents who make regular trips back to retrieve personal items, collect mail and feed pets say they are unaware of anyone still living in properties on notice.