|The death toll from the last earthquake has risen to 166, with a possible further 80 people unaccounted for [EPA]
Some 10,000 homes in Christchurch are to be demolished because of earthquake damage, while some parts of the city will have to be abandoned altogether, New Zealand's prime minister said.
In addition, several hundred commercial buildings will also be pulled down, John Key said.
"Potentially there are some ... areas of Christchurch which will need to be abandoned and we will have to provide other alternatives for people to live in because the land has been so badly damaged, we can't fix it - certainly not in a reasonable time frame," Key said.
The number of 10,000 includes 3,300 homes that were damaged by an earlier magnitude 7.1 quake on September 4 that caused far less damage.
The magnitude 6.3 quake that hit on February 22 shattered homes, heritage buildings and office blocks, and caused 166 confirmed deaths.
Officials expect the toll to rise to more than 200 as rescuers continue to search for bodies in the rubble.
Earthquakes can cause sections of earth to liquefy and push up to the surface as watery silt, a process called liquefaction. In Christchurch, 260,000 tons of silt have already been scraped away.
"There are some parts of Christchurch that can't be rebuilt on" due to damage from liquefaction, Key told reporters.
He said modular homes will be brought in to provide temporary housing for some of the many thousands of displaced.
Rugby stadium damaged
Key also said he should know "within a few weeks" whether Christchurch's damaged rugby stadium can be repaired sufficiently to host World Cup matches later this year.
"There's some damage to the Deans Stand, some damage to the Hadlee Stand, there's some liquefaction outside and the turf has liquefaction damage which means it needs to be rebuilt - and that takes quite a number of months."
He said Christchurch's chance of hosting five group matches and two quarterfinals was not "looking bleaker" but there were several issues to be addressed before a definite answer could be given.
Keys said if the problems with the stadium could be fixed, then other logistical issues could be addressed.
"In the end, if we can get a stadium that operates and everyone is comfortable with then ... we need to deal with accommodation issues and with bars, restaurants and the like.
"I think we can address those issues, but we can't do that unless we have a stadium that gets a tick off."
Work crews are still clearing rubble from the earthquake, which badly hit the downtown area and cut water and power services across the city.
Almost all electricity supplies have been restored, but residents in the city are being told to boil tap water because of the risk of contamination.
Officials say some 70,000 people - one-fifth of Christchurch's population of 350,000 - have left the city temporarily as a result of the quake.
A national memorial service is planned for March 18, and Key said the open-air service in a city park could attract up to 100,000 people.