The Crown has bought the Christchurch property where the Pyne Gould Corporation building stood until it collapsed in the February 2011 earthquake.
The purchase has been made to incorporate the property at 233 Cambridge Terrace into the new North Frame as part of the post-disaster Christchurch Central Recovery Plan.
In recognition of the significance of the site - where 18 people died and many others were seriously injured - the Christchurch Central Development Unit has written to the families of those who lost their lives to inform them of the development.
Unit director Warwick Isaacs said the sensitivities involved with the site have been an important consideration for those involved in the planning of the North Frame.
"That is why we have been in contact with those affected families we have contact details for - to let them know about the change in ownership and to reassure them that access to the site will not change in the near future," Mr Isaacs said.
"Decisions are still to be made about the longer term use of the site, but those involved in the design and planning for the North Frame have been very mindful of what occurred at the PGC site, and this will be reflected in any decisions that are made.
"I have committed to keeping those families informed on the key decisions that are made about the site."
In July, the unit announced the Crown had bought the site where the Canterbury Television building stood, for incorporation into the East Frame. A total of 115 people died in that collapse.
The future use for the PGC and CTV sites is a separate issue to the planning for the city's earthquake memorial, the unit said.