ChristChurch Cathedral – the icon of that quake-crippled city, and the most recognised church in New Zealand – is to be deconsecrated ahead of partial demolition.

Bishop Victoria Matthews confirmed in a press conference in Christchurch today that the cathedral would have to be partly demolished, and further engineering measures taken to make the rest of the building safe.

Until the demolition work is actually underway it won't be clear how much more of the cathedral will have to be brought down.

But Bishop Matthews says some part of the structure may be able to be retained.

This controlled demolition work – expected to cost $4 million – will also allow some of the cathedral's treasures to be removed and stored until decisions are taken about a future cathedral.

"The decision," said Bishop Matthews, "follows a challenging and complex assessment process including review and input by a range of involved and interested people to identify options and risks, along with consideration of expert analysis and technical reports.

"At all times we have proceeded with a deep commitment to being faithful to the gospel we proclaim.''

The 120-year-old cathedral withstood violent earthquakes in 1881, 1888, 1922, 1901 and on September 4 last year.

But it couldn't ride out the 6.3-magnitude earthquake in February – which killed 182 people and reduced the cathedral's spire to rubble – and it suffered further major damage in the June 13 jolt.

The west wall of the cathedral partially collapsed then, and the rose window above the west doors was destroyed.

Media conference

During a joint media conference in Christchurch this morning with Gerry Brownlee, the Earthquake Recovery Minister, and Roger Sutton, the CEO of CERA, Bishop Matthews said the extent of the damage makes the building unpredictable and unsafe - particularly in the event of another quake.

Making it safe again was a key concern for the Church Property Trust (CPT), which is the steward of the cathedral on behalf of the Anglican Diocese of Christchurch.

Before the controlled demolition work is carried out, Bishop Matthews will deconsecrate the cathedral.

Taking that decision hadn't been easy.

"No one," she said, "loves the cathedral as much as we do.

"However, this is the next step towards a decision about the future of the cathedral, which will combine the old and the new.''

In another sense, the deconsecration means that the Bishop of Christchurch will no longer have a home base: the word cathedral derives from the Greek word 'kathedra', meaning seat - and the teaching seat of the bishop is a centrepiece of every cathedral.

Bishop Matthews says it is "critically important'' to the bishop, dean and the Anglican community of Christchurch that the right decision is made about the church's base in the city in the short and long term.

A number of options for interim cathedral ministry – including the idea of a cardboard cathedral – are being considered.

English architect

ChristChurch Cathedral was consecrated on November 1, 1881.

It was designed by English architect George Gilbert Scott, but Benjamin Mountfort – perhaps the foremost Gothic Revival architect in New Zealand – supervised the work.

While ChristChurch Cathedral is obviously based on European cathedrals, it does also feature local influences, including matai and totara from Banks Peninsula, and stone came from local quarries.

Those influences could also be seen in the interior: with Maori and Polynesian taonga adorning the cathedral's walls, and local flora and fauna in stained glass and in carvings.

Structural engineering and heritage experts gave the CPT and Cathedral Chapter a number of 'make the building safe' options, ranging from complete demolition and cleared site, through to a controlled demolition, maximum salvage and storage and an ultimate full reconstruction.

As noted earlier, the controlled demolition and 'make safe' option chosen will cost about $4million.

The professionals have also advised the CPT that any of the "future scenarios (for a new or rebuilt cathedral) have a funding shortfall of at least $30 million."