Fletcher Construction says there is no one single register with figures on how many people in Canterbury may have been exposed to asbestos through earthquake repairs.
A project manager for a company accredited to Fletcher EQR to manage EQC repairs in the Canterbury Home Repair programme claims that up to 60,000 people could have been exposed to lethal asbestos fibres.
Homeowners of quake-damaged houses are made aware of asbestos problems, but there is no single registry of all the asbestos homes across Canterbury.
Fletcher Construction chief executive Graham Darlow said on Wednesday that records of asbestos homes were kept by its unit Fletcher EQR and the Earthquake Commission.
Mr Darlow said a single registry would come with a cost and the agencies involved would need to discuss whether it was good use of public money.
He defended how staff have handled the removal of asbestos in Christchurch home repairs since the damaging quakes began in 2010 and 2011.
Mr Darlow told Radio New Zealand's Nine to Noon programme all houses built between 1940 and 1990 that have been or are being repaired were tested for asbestos from the middle of 2012. He said 35 home owners have requested a further test following their repairs. He said out of the six investigations by industry regulator WorkSafe, five have not resulted in prosecution and one was ongoing.
"We've been engaged in this programme since the first earthquake in 2010 and we've completed 48,000 emergency repairs, and we've now completed a further 56,000 permanent repairs so I don't think six is a big number across that."
The Earthquake Commission said it is more than satisfied with how Fletcher EQR has handled asbestos.
Earthquake Recovery Minister Gerry Brownlee on Wednesday announced a multi-government agency review into the processes of dealing with asbestos.
The review is being carried out by the Ministry of Business, Innovation and Employment, the Earthquake Commission and Fletcher EQR.
Mr Brownlee told Nine to Noon he was confident with the processes in place for handling asbestos in Christchurch house repairs. He said previous issues regarding asbestos have been successfully and appropriately dealt with, and government agencies were doing what they have always done and were working together.
The minister said no one was trying to sweep the issues under the carpet or hide, and agencies who have been doing the work were doing a good job.
Christchurch's Medical Officer of Health Alistair Humphrey said anyone affected by asbestos would be at risk of developing the cancer mesothelioma.
Dr Humphrey told Radio New Zealand's Morning Report programme that 90 percent plus of people won't have been exposed, but Fletchers needs to reassure homeowners they were safe from any risk.
Ian Shaw, a Professor of Toxicology at Canterbury University, doubted that asbestos had been handled safely in the demolition and repair of quake-affected buildings.
He told Radio New Zealand's Checkpoint programme anecdotal evidence suggested that removing the substance safely has not been a top priority.
"I've seen quite a lot of dust rising up from demolition sites that needn't necessarily be asbestos - and I hope it isn't. But demolition dust in its own right, concrete dust has a very similar effect, and that suggests to me that people aren't thinking seriously about this."
Professor Shaw said he predicted several years ago that asbestos exposure could be an issue in the years after the Christchurch quakes.