New Zealand police said Tuesday they will proceed with a criminal investigation into the catastrophic collapse of an office block in the 2011 Christchurch earthquake which claimed 115 lives.

The CTV building crumpled then burst into flames after the 6.3-magnitude tremor on February 22, 2011, killing those trapped inside, including 65 foreign students mainly from Japan and China.

A Royal Commission concluded in 2012 that the six-storey 1980s-era office block was so badly designed it should never have received a building permit.

Designed by an engineer with no experience of multi-storey structures, its steelwork was not constructed properly and the local council failed to pick up on the problems.

As a result, the building "pancaked" within 20 seconds of the tremor hitting, accounting for almost two-thirds of the 185 deaths in New Zealand's worst quake for 80 years.

Since the commission's report, police have been assessing evidence to weigh up if a criminal investigation was warranted.

They said Tuesday that a criminal probe would proceed, with manslaughter charges a possibility against those responsible for the structure.

"Bearing in mind that 115 people died, (manslaughter) is the principal charge we're focusing on," Detective Superintendent Peter Read told reporters. "It's got to be supported by the facts and we're still a long way from that yet."

Police said it was too early to say when the investigation would be completed.