The Earthquake Commission believes 50 homes in Nelson and Tasman will have to be completely rebuilt as a result of last week's flooding.
The commission says it could receive as many as 1000 flood-related claims.
It says its estimate of properties that may be beyond repair comes from information from the Nelson city and Tasman district councils.
It has received 588 claims and says the number could reach 1000 as owners of holiday properties return to the region to find damage.
The commission says damage ranges from broken pipes to serious slips.
It says it has 22 assessors in Nelson until Christmas, and they will return after a break.
It expects to complete assessments of all damaged properties by mid-January.
Civil Defence says 64 properties remain with red-stickers, meaning they are unsafe to enter.
Some residents frustrated
Tasman mayor Richard Kempthorne says people affected by slips from last week's record rain are starting to get frustrated they can not clean up their properties.
Engineers are allowing 12 homeowners to return home after a second assessment of their properties.
But 44 houses are still too dangerous, and 49 more have yellow stickers - meaning restricted entry only and their owners cannot live in them.
Mr Kempthorne says although some people have been allowed to return, they cannot clean up slip material from their backyards.
He says that's because removing material from the bottom of a slip could result in destabilisation of material further up the slope.
Mr Kempthorne says that's frustrating for people who want to clean up their properties.
But he says geotechnical engineers are continually reassessing the situation.