Civil Defence Minister John Carter says it could be a week before a full assessment of earthquake-damaged houses in Canterbury is completed.
Mr Carter says about 100,000 of the 160,000 homes in the Waimakariri, Selwyn and Christchurch areas are damaged. It is not clear how many of these are unfit to live in.
He says welfare centres will remain open for as long as they are needed and that alternative accommodation may be considered.
Mr Carter says people still need to boil water but the supply could be back to normal within two weeks.
He says repairs to the sewerage system are going to be far more challenging, and portable toilets will be distributed throughout the city to help deal with the problem.