Canterbury police have interviewed over 100 witnesses as the investigation continues into the collapse of the CTV building.

115 people died when the building collapsed in the 2011 February earthquake.

Large amounts of information are being collated and a number of search warrants issued in the investigation, as police examine whether there's criminal liability.

Engineering consultants BECA are providing expert advice, with the investigators creating a physical rebuild, to test critical elements of the building's structure.

Though police can't confirm a time frame, it's thought a final decision will be made later this year.

Detective Superintendent Peter Read said the investigation has progressed significantly, with a large amount of information from a range of sources collated and evaluated.

He said the enquiry team is now using another consultant engineer as well as a solicitor as part of the investigation.

Peter Read said it remains to be a complex investigation and a number of key areas need to be finalised before any assessment of liability can be discussed and advanced.

Families have been kept up to date with the progress.