Bishop Victoria Matthews of the Anglican Diocese of Christchurch said: "The cathedral will be deconstructed with the utmost care and respect while at the same time protecting the treasures within its walls - there will be no bulldozers or wrecking balls on the job.''
The brutal safety measures will allow the retrieval of taonga and heritage items.
Rev Matthews said a rebuild was not feasible, as was a replica cathedral, saying it would cost more than $100 million.
"We would not be responsible stewards if we ignored the financial realities,'' she said.
"The Anglican Diocese is facing a hard reality _ the cathedral is the revered `Mother Church' but is not the only church in the Diocese to have sustained damage, in some cases irreparable or too costly to repair.''
She could not rule out a full demolition admitting: "It is in the realms of possibility, but it is not desirable.''
The church said the deconstruction would likely be completed by the end of the year.
A new "beautiful, inspiring, safe'' cathedral would be built somewhere, but it would take "years, not months.''
"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. However, this is now a very dangerous building that needs to be made safe.''
The 131-year-old cathedral withstood violent earthquakes in 1881, 1888, 1922, 1901 and even September 4 last year.
Christchurch mayor Bob Parker said the news would be "heartbreaking'' for many people in Christchurch.
"We all have a sense of ownership in this building. This has not been an easy decision for the church. It is not an easy decision for many of us to accept either.''
Heritage campaigner Neil Roberts, of the Christchurch Civic Trust, was critical of the church's decision, arguing more time should have been taken to consider other options.
"Engineers from overseas who are experienced in earthquake strengthening have said 'Of course we can save parts of this building'. We don't have to deconstruct it or pull it right down. But they are not listening to that.''
The Wizard of Christchurch described the decision as "an unforgivable act of barbarism''.
Ian Brackenbury Channell, 79, has performed in front of the central city landmark building in Cathedral Square for decades.
He has started a petition against the demolition.
He said the decision would "spark a huge uproar'' from Cantabrians.
"To knock it down is an unforgivable act of barbarism.... so crude, vulgar, insensitive, and shows a complete lack of appreciation of beauty.''
The New Zealand Historic Places Trust also expressed its disappointment, saying the building could have been restored or rebuilt in a recognisable form.
"The church's decision to deconstruct the cathedral down to sill level or a maximum of two to three metres around the full extent of the building will make it very difficult to retain any sense of this very important building as it once was,'' NZHPT chief executive Bruce Chapman said.
"The NZHPT would have preferred the option which sought maximum safe retention of the building's heritage as a basis for rebuilding the cathedral in a recognisable form.''
But Earthquake Recovery Minister Gerry Brownlee called the decision a "courageous'' one.
"We've got to remember that the Christ Church Cathedral does somewhat define the city, so it's a very, very sensitive building. The real challenge now is work out the shape of the building that defines us going forward.''
- Additional reporting nzherald.co.nz
