WELLINGTON: New Zealand police on Thursday ruled out laying criminal charges over the catastrophic collapse of a office block that claimed 115 lives in the 2011 Christchurch earthquake.

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.

After a four-year investigation, police said they did not have enough evidence to proceed with negligent manslaughter charges against the engineers responsible for the building.

"The evidence available is not sufficient to provide a reasonable prospect of conviction in court," police said in a statement.

The building's collapse accounted for almost two thirds of the 185 deaths in New Zealand's worst quake for 80 years, which flattened the downtown area of the South Island's largest city.

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.

It had also been damaged in two quakes which preceded the deadly February tremor, something the local council failed to pick up, allowing it to remain occupied.

The building "pancaked" within 20 seconds of the quake hitting and was engulfed in an inferno so intense that forensic experts had to use DNA testing to identify the remains of many victims.

Police said the investigation raised issues that were "delicate and finely balanced" but ultimately the evidence was not strong enough to take to court.

"We are acutely aware that there will be disappointment with this decision, particularly for the families and friends of those who died in this tragedy," they said.-AFP