Christchurch's Anglican cathedral will be demolished after suffering major damage in the earthquakes that rocked the New Zealand city over the past year, church officials said Friday.

The spire of the 131-year-old cathedral, a symbol of the South Island city, collapsed in the February 2011 quake that killed 185 people, with the structure sustaining further damage in subsequent quakes in June and December.

Bishop Victoria Matthews said the cost of saving the cathedral was "staggering" -- an estimated NZ$50 million ($42 million) to rebuild using existing parts of the building or NZ$100 million for a complete reconstruction.

She said the cathedral remained too dangerous to enter and the risk of more earthquakes in Christchurch meant repairing the revered building was not an option.

"The cathedral will be deconstructed with the utmost care and respect, while at the same time protecting the treasures within its walls," she said.

"There will be no bulldozers or wrecking balls on the job."

Matthews said that the first priority was to pull down the walls to a level of about 2-3 metres (6.5-10 feet) so artworks and other treasures could be safely removed.

She said the church was committed to creating "a beautiful, inspiring, safe new cathedral" but no decision had been made on where it would be built and what it would look like.

The cathedral lies in the city centre "red zone", the worst-hit area during the quakes, which remains off-limits to the public because the risk of falling masonry makes it too dangerous to enter.

The cathedral's future had been the subject of heated debate in Christchurch, with some arguing it should be saved at any cost as a symbol of the city's endurance after its earthquake ordeal.

Christchurch city councillor Aaron Keown vowed to stop the demolition and said there was widespread support for his position in the community.

"I would be in there chaining myself to the building to stop that and I know lots of other volunteers would come in to do that," he told the Christchurch Press.

Matthews said she recognised there were strong feelings in the city about the issue but said the church "would not be responsible stewards if we ignored the financial realities".

"We acknowledge the high level of community interest and sense of ownership as the cathedral was both an iconic building and a place of regular worship by many," she said.

"However, this is now a very dangerous building that needs to be made safe."

The fate of Chirstchurch's 1905 Catholic Cathedral of the Blessed Sacrament is yet to be determined but reports say the renaissance-style building faces a NZ$10 million repair bill.