The Christchurch City Council and the Government are looking to buy 16 green-zoned properties on the Port Hills that have been identified as being at risk from landslides.
New council-commissioned GNS Science reports released today show 37 green-zoned homes are in areas where the risk to life from landslide -- also known as "mass movement" -- is considered 'intolerable' by the council.
A further 21 homes will undergo remedial work over the next 12-15 months to protect them.
The latest reports look at what could trigger a landslide, how big it could be, where and how the land is likely to move and, crucially, the level of risk to people.
"With peoples' safety coming first, we are making some tough decisions about land use and development in these areas," said the council's chief planning officer Mike Theelen.
Mayor Lianne Dalziel said the decisions will be "very welcome for some" but "upsetting for others".
"We will be supporting all these Port Hills residents in the coming months," she said.
"I am delighted we can work with the Crown to fund engineering solutions to see as many people as possible remain in their homes."
There are also 89 properties in Class I mass movement areas that have already been red-zoned by the Crown for cliff collapse or rockfall.
Of these, 76 are owned by the Crown and 13 of them remain privately owned.
The new information does not change any red zone offer from the Crown.
While the risk to people in Class I areas was described as "intolerable," there were no signs that slope failure was imminent, so residents were not being asked to leave their homes at this time, Mr Theelen said.
"We are monitoring known mass movement areas and if there is a change in the behaviour of the slope and increased risk to people's safety, we will act swiftly," he said.
"This may mean people may need to leave their property at short notice.
"These investigations have taken longer than we anticipated. The findings needed peer review by an international team of experts, to ensure the science was robust enough to support sound decisions about people's lives and homes."