Soaked Nelson residents are bracing for more heavy rain this afternoon as authorities study historical slip sites amid the threat of another torrential downpour.
Some roads at Dovedale, near Richmond, are already "flooded and fast flowing", Nelson-Tasman Emergency Management Group spokeswoman Angela Ricker said this morning.
Tasman District Council has warned Motueka residents to boil their water for at least one minute before drinking it and those cleaning up after yesterday's deluge are being warned to take care of mud and silt that may be contaminated by sewage.
There have been about 500 calls to emergency services since yesterday afternoon when the region was inundated with 104mm in one hour, the second-highest rainfall recorded in one hour.
Fire Service southern communications centre shift manager Riwai Grace said most calls were for flooding in the Nelson-Tasman area, including a medical emergency when someone received an electric shock while trying to turn the water off in their flooded property.
Numerous people had been rescued from their flooded homes and firefighters were assisting rest homes stricken by the rising water overnight.
Mr Grace said the huge volume of calls meant emergency services had to prioritise which incidents they attended first.
"We've been asking whether the flooding is inside or outside the property - if it's outside they go to the bottom of the list. If it's inside we ask if they're trapped in which case we get them to the top of the list, or if they're elderly. If it's not a priority we've been trying to give them advice on how they might be able to stop it [the water] themselves.
The weather had improved this morning and there had only been about four calls so far, but with the rain forecast to return today emergency services were bracing themselves for another onslaught.
"I'm now touching wood that those people up there will get some respite, but who knows," Mr Grace said.
MetService meteorologist Dan Corbett said another subtropical trough was expected to pass over the region later this afternoon.
It was this morning raining on the hills around Nelson and it would likely move into the city soon, he said.
"Through the middle of the day and into the afternoon around the northern South Island and also Taranaki they're under the gun again for some of these heavy downpours," Mr Corbett said.
It was likely to pass by this evening, and cooler, fresher air would start coming in from the Tasman, possibly bringing more rain but in far lesser quantities.
"We get through this evening and then we at least lose this heavy, sub-tropical moisture," Mr Corbett said.
Much of the country, from Waikato to Buller, could possibly see thunderstorms from the mid to late afternoon today.
Ms Ricker said several families had sought assistance at a welfare centre set up at the Richmond New Life Centre this morning.
The extent of the damage to properties and infrastructure was still being assessed.
Saxton Field and Saxton Stadium in Stoke were closed due to flooding, as was the Rabbit Island Recreational Reserve.
