Nelson Civil Defence has evacuated 30 homes above Rocks Road that are threatened by a massive slip in the aftermath of the region's worst rainstorm in 50 years.
The organisation says the huge slip behind the houses on Grenville Terrace is cracking and opening up and residents have been asked to leave as a precaution.
Civil Defence has inspected about 90% of the storm-battered homes in the area that have registered for a visit, most of which are in Nelson itself, and by Sunday night 91 of them had been red stickered.
Group controller for Nelson-Tasman Alec Louverdis says the main pipeline supplying water to Nelson is still under threat of being damaged.
He says if the two slips below the pipe fall, the pipe will go with them, restricting water supply to the city.
Cable Bay still isolated
Mr Louverdis says another priority is to start work on clearing the road to Cable Bay, which is 15 minutes drive east of Nelson city, and get food and water to the stranded residents.
He says it will take at least a week to have one lane of the blocked access road cleared, and even then it will be open only to residents.
Supplies were sent in on Saturday by helicopter and residents were finding other ways of getting material in, including by boat from Nelson.
Altogether, last week's floods have forced the evacuation of 300 people in the Nelson-Tasman area and 60 families have registered for assistance.
Civil Defence welfare manager Susan Coleman says there have also been evacuations in Golden Bay.
Businesses hit hard
Businesses in Nelson-Tasman are concerned at the impact of last week's storm as the peak summer holiday season approaches.
A state of emergency is expected to remain in place for some time in areas including Golden Bay, Nelson city and Richmond.
The owners of a holiday park in Cable Bay say they will face a major loss of income if the road to the area remains cut off for weeks at the peak of the summer break.
People in the popular summer holiday settlement of Pohara in Golden Bay are still without water and sewerage following the torrential rainfall.
Pohara bore the brunt of the heavy rain and a torrent of mud swept through 20 homes and the camping ground, which has had to close because it has no power or sewerage.
The damage to the water treatment plant cannot be fixed, and water and portaloos have been delivered to the tennis courts at Pohara Hall.
People have been urged to boil water, but Mr Louverdis says 95% of residents should have non-potable water supply by Christmas.
Business people who rely on the summer trade are anxious to get the water back on so restaurant and cafe kitchens can operate, and toilets can be used.
In nearby Ligar Bay, residents have been digging out after a 20 metre wide slip crashed through their homes, in one case submerging the entire first floor of a two-storey home in mud.
Ban on swimming and shellfish gathering
A temporary ban has been imposed on swimming and shellfish gathering in the Nelson and Tasman areas.
The ban covers Tahunanui Beach, all beaches on Rabbit Island and Rough Island, Ligar Bay, Pohara Beach and Tata Beach, and all beaches at Motueka.
Nelson-Tasman Civil Defence spokesperson Angela Riker says whenever there is heavy flooding, beaches need to be treated with caution.
She says it is not yet known when the ban will be lifted.
Civil Defence says occupants of homes with stickers may be able to move back in time, but their houses are not habitable at present.
Logging may be to blame - O'Connor
West Coast Tasman MP Damien O'Connor says logging practices may be to blame for the floods in Pohara.
Mr O'Connor says logs left behind when trees are felled form dams in gullies in the hills above the township.
He says water builds up after heavy rain and is then released in dangerous torrents.