An inspection of Christchurch Arts Centre buildings has revealed many were five to 10 seconds from collapse in the February earthquake.

Every historic building on the Arts Centre site was badly damaged in the quake.

The Christchurch Boys' High School building, the Great Hall, Rutherford's Den, the Clock Tower, the library building (SOFA Gallery) and the hydraulics building (Southern Ballet) have significant internal cracking, shifted walls and floor damage.

Strengthening work on the historic Clock Tower and Great Hall could start in three months.

An internal wall in the former Boys' High building had to be taken down after it moved when a contractor touched it, and artefacts in Rutherford's Den were damaged.

Holmes Consulting Group project director John Trowsdale said internal assessment of the buildings was possible only after they were shored up.

"As a whole – and it becomes apparent as we look inside – the site came very close to collapse. It was five to 10 seconds away from a reasonably significant collapse," he said.

"The Southern Ballet building took an absolute hammering. When you look inside, you see how close it came to significant collapse."

Engineers have been investigating how to repair and strengthen the Great Hall and the Clock Tower.

Trowsdale said the work could include large stainless-steel rods drilled vertically and horizontally into walls to create a reinforcing web.

Sections of the Clock Tower may have to be taken down and rebuilt stone by stone, but Trowsdale said deconstruction was a last resort.

Arts Centre director Ken Franklin said the Clock Tower and the Great Hall were the most important heritage assets on the site.

Computer models of the two buildings were being used to calculate how the buildings responded to the quake and the best way to strengthen and rebuild them.

An internal inspection of the Dux de Lux building showed a concrete beam above the bay window in the Brew Bar was close to collapse.

"It is only just holding on. It is resting on a wee half-brick," Trowsdale said.

Aftershocks continue to cause damage to the Arts Centre.

The magnitude-5.5 quake on Monday toppled a piece of masonry from the north gable of the Great Hall.

Small pieces of glass are fixed to walls to measure any movement from aftershocks. If the wall shifts significantly, the glass will break.

Trowsdale said he focused on one part of the Arts Centre site at a time.

"I would go nuts if I started thinking about the whole problem," he said.

- © Fairfax NZ News