A specialist dam engineer overseeing the precautionary drainage of the Haldon Dam has discovered more issues with its stability.
After Friday's tremors the Marlborough District Council made the decision to lower the water level in the dam in the interest of public safety.
Emergency services were now on standby in Seddon and nearby residents have been warned, the Council's assets and services manager Mark Wheeler said.
In a worst-case scenario, eight rural properties, about a dozen houses and around 20 sections in Seddon's township on the south-east side of Starborough Creek could flood if the dam breaches.
Property owners have been advised they would get 90 minutes' notice if floodwaters were going to flow into Starborough Creek toward their properties.
A warning note was delivered to households this afternoon advising occupants of the increased risk and the possibility of being asked to evacuate.
Emergency services would move door-to-door evacuating properties should that be required, Mr Wheeler said.
Extreme flooding was unlikely, according to the engineer's advice.
Heavy weekend rain had slowed the drainage of the dam.
Meanwhile, eight Seddon houses must be vacated because they have been deemed unsafe or uninhabitable by Marlborough District Council building inspectors. Another 11 have restricted use only because of safety issues.
An inter-agency meeting in Seddon today discussed the anxiety issues that were expected to emerge as people grasped the extent of the damage, the Council said.
Victim Support, Age Concern Marlborough and the Red Cross all had resources available.
Farmers were urged to contact the Top of the South Rural Support Trust if finance problems or stress levels were increasing, the Council said on its website.
Marlborough Mayor Alistair Sowman said he had been advised that a few people are using garages, tents or caravans for shelter, and offers of accommodation were coming in.
"The community has been looking after each other very well but we know that, as exhaustion sets in, some people will find it hard to keep positive. I urge anyone who needs help to ask for that support."
Tower Insurance said it had received a small number of calls so far from customers in Wellington and the Marlborough region affected by the earthquakes.
Westpac Stadium management were yet to confirm whether they had been given the all clear from engineers for the All Blacks vs Wallabies game on Saturday.
Cook Strait quake forecasts:
* Magnitude 6 and above: in the next 24 hours - 3.5 per cent / this week - 14 per cent
* Magnitude 5 to 5.9: in the next 24 hours - 30 per cent / this week - 76 per cent
* Magnitude 4 to 4.9: in the next 24 hours - 98 per cent / this week - over 99 per cent
- Brendan Manning and Rebecca Quilliam of APNZ
