People need to be held to account over the collapse of the CTV building, Prime Minister John Key says.

Speaking in Auckland this afternoon, Key was asked about a police investigation, believed to be under way into Gerald Shirtcliff, the man who supervised the construction of the Canterbury Television (CTV) building.

"I wouldn't want to comment on that," Key said.

However, he said the CTV site was "a place of great tragedy".

"People need to be held to account. That would be the expectation for New Zealanders, if there is a catastrophic failure and there is criminal liability the police would follow up on that, but that is a matter for them."

The CTV building was finished in about October 1987. It collapsed on February 22, last year, taking the lives of 115 people, when Christchurch was hit by a magnitude-6.3 earthquake.

The Canterbury earthquakes royal commission has been told of a number of construction defects with the building, although Shirtcliff denies he had much to do with the site.

Early today a police spokesperson said Police National Headquarters had received a complaint which was being assessed and a senior investigator had been assigned to look into the matter.

No other details were immediately available.

A month-long investigation by The Press shows Shirtcliff in 1970 stole the identity of an English engineer called William Anthony Fisher, with whom he worked in South Africa in 1968 and 1969.

Shirtcliff has lived as William Fisher in Australia for over 25 years, and now resides in Brisbane, driving a late-model Mercedes and enjoying a spacious house and a $200,000 motor launch.

When Shirtcliff left South Africa towards the end of 1969 to settle in Sydney he took on Fisher's identity including his birthplace, birthdate and his bachelor of engineering from the University of Sheffield.

Shirtcliff then used the real Will Fisher's BEng to gain entry into a masters programme at the University of New South Wales in 1971 and also to become a member of the Australian Institute of Engineers in 1972.

As "Will Fisher" he was awarded a master of engineering science degree in highway engineering in April 1974.

Building and Construction Minister Maurice Williamson has told Radio New Zealand it may be possible for the Government to seek an extradition order for Shirtcliff.

If an investigation suggests a prosecution is warranted, Williamson said moves may be made to get Shirtcliff to face charges in this country.

But he warned "there is a lot of water to flow under the bridge".

Shirtcliff could face "pretty serious'' charges if police find there is a case to answer, Williamson said this morning.

He said he was not prepared to let the allegations go unanswered.

He also revealed he had asked his ministry to review its systems but said the incident involving Shirtcliff had happened many years ago and systems were now more robust.

Williamson agreed the allegations about Shirtcliff may not have been revealed had it not been for The Press' investigation, but suggested it would have come out eventually.

Srecko "Alec" Cvetanov, who lost his wife Tamara in the CTV building collapse, said he welcomed the investigation.

However, Cvetanov questioned how Shirtcliff's fake identity jeopardised the integrity of the building and he was concerned the public was simply "thirsty for justice".

Cvetanov felt there were "multi-dimensions" that were responsible for the failure of the building.

- © Fairfax NZ News