The owners of two buildings destroyed by the last week's earthquake both say they had engineers carry out structural checks after the 4 September quake.
The Government is signalling there will be an inquiry into the collapse of the the Pyne Gould and CTV buildings, and owners of both say they will fully co-operate.
The central city buildings were cleared for occupation after the 4 September quake. They were given green stickers, meaning they had passed an external check and their owners could return.
Prime Minister John Key says the Department of Building and Housing is already looking generally at how buildings are cleared, and a wider inquiry is on the horizon. It will look at how buildings collapsed and whether the building code is adequate.
Mr Key says he has asked for advice on the best way to proceed, and expects to have more information by the end of the week.
Building 'deemed secure'
White Fox Jones, the law firm acting for the owners of the CTV building, says the building was inspected after the September quake and deemed secure for occupation.
It says Christchurch City Council building manager Steve McCarthy then commissioned a structural engineer's report that raised no issues regarding the structural integrity of the building.
A spokesperson for the law firm, Ken Jones, says an inquiry is therefore important to establish why the building collapsed, so that something like this cannot happen again.
And a lawyer speaking for the family trust which owns the Pyne Gould building says four assessments and reports were made after the first quake, and the Boxing Day aftershock.
The City Council says it believes the CTV and Pyne Gould buildings were checked by private inspectors in September, but is unsure whether buildings given the all-clear were checked by engineers before being reoccupied.
A green sticker places the onus on the building owner to carry out an engineer's inspection, it says, but no proof of such an inspection was required.
The council says it expected to be advised by the owners if there were any safety issues but it never was. Mr McCarthy says the checks were expected to be done in good faith.
He says only the owners of buildings that received a yellow or red sticker were required to submit engineering reports to the council.
Work to repair superficial damage to the CTV building from September's earthquake had been under way at the time last week's collapse.
Meanwhile, police say part of the Pyne Gould building will have to be brought down because of worries about its stability.
Lasers used by crews at site
Crews working at the Pyne Gould building have put an alarm system in place that is triggered if the structure moves by as little as two centimetres.
The head of the British search and rescue contingent, Sean Moore, says lasers have been placed on the building to detect any movements in what is a dangerous working environment.
Mr Moore says safety is paramount for crews dealing with the risk of aftershocks and asbestos contamination.
Mr Moore says about 20 victims have yet to be found at the site.
Civil Defence has assessed the safety of more than 12,000 properties in Christchurch.
Civil Defence co-ordinator Steve Frasier says that as of Tuesday 1,445 have been declared unsafe and bear a red sticker.
About 2,100 have been given yellow stickers, which restricts access, and the majority - nearly 8700 properties - have green stickers, meaning they are cleared for normal use.