Waitaki Civil Defence authorities said this cold front, which could also bring snow to 200m in parts of South Otago and Southland, was expected to be followed by another from the east which could bring heavy snow to North Otago and Canterbury tomorrow evening.
Although rivers were slowly falling they were still high, and surface flooding remained a problem throughout the district.
"We still advise the public to avoid non-urgent travel, as many roads across the district remain impassable," spokesman Richard Mabon said.
Supplies of bread and milk were running low in Oamaru because delivery truck had been unable to reach the town.
It was hoped supplies would be refreshed tonight.
Rain had caused a rock fall at the Ngai Tahu Maori Rock Art site, south of Duntroon, and visitors to the site were warned not to enter.
Rescue teams helped by the New Zealand Army have reached properties isolated by floodwaters in North Otago as road access to Oamaru reopens from the south.
Rescuers have called for specialist equipment to help pump water out of a property surrounded by water at Awamoko, 26km northwest of Oamaru, a Waitaki District Civil Defence spokesman said.
They have also reached another rural property at Robb's Crossing and confirmed a family cut off by water are fine, the spokesman said.
As rain continues and snow and cold threatens, Civil Defence is encouraging people to check their neighbours and look out for each other.
"Contact with neighbours should not stop even though the rain might ease off," said Civil Defence spokesperson, Richard Mabon.
"Friendly company can be a great help and support. A chance to talk, see a friendly face, have a cup of tea together can be a great reassurance at a time of stress."
Soldiers and two Unimogs are helping access areas cut off by heavy rain.
Two Iroquois helicopters were also on standby as steady rain continued to fall, and snow forecast to hit low lying areas.
Heavy rain isolated Oamaru yesterday and an evacuation assembly point was set up in Kakanui, 11km away.
Many kindergartens and schools were closed today and school bus services had been cancelled.
Mr Ridley said the rain had compromised water quality and residents on rural water supplies should boil their water and conserve as much as possible.
Timaru District Council acting public information manager Philip Howe said the area was lashed by heavy rain overnight and several roads in the Levels, Arowhenua, Milford/Clandeboye, Rosewill and Washdyke areas had been closed.
Mr Howe said more rain was forecast for today and residents in low-lying areas should be prepared to move.
Unnecessary travel should be avoided and all schools in Temuka and Pleasant Point were closed, he said.
An Environment Canterbuy spokesman said the area was "over the worst of it" and most rivers had peaked late last night or early this morning.
"We've just really got to keep an eye on what the intensity of the rainfalls are going to be for the rest of the day," he said.
Wellington emergency services were kept busy late last night as flooding swept cars down roads and put residents on evacuation alert.
Water flowed on to properties in the northern suburb of Tawa, as well as in Porirua's Titahi Bay, forcing Civil Defence to prepare to evacuate houses from 9pm.
Several roads around Titahi Bay were closed as surface flooding sent cars floating down them.
"There were a couple of places where cars were bobbing around," police central communications Inspector Mark Oliver told NZPA early this morning.
"You're talking about a fair amount of water to float a car. Although it may not necessarily be the depth, it may be how fast it's flowing, because if it's where the water has breached the river banks then it generally does that in a fair rush."
However, roads reopened and evacuations were avoided as the heavy rain subsided.
"It seemed to come on very quickly then die down very quickly," Mr Oliver said.
"House evacuations that were going to go ahead never did in the end, so that was good, and by about midnight we heard the last of any major issues.
"I'm sure there are areas of surface flooding out there, but nothing that's causing any issues for us."
Mr Oliver said he was not sure if any houses had been damaged by flooding.
"There were a couple of properties that certainly had water flowing into them, but I'm not sure if anything breached into houses."
Canterbury, Otago and the Bay of Plenty were also on alert overnight as the wet weather continued to affect many parts of the country.
Whakatane police said the heavy rain that had been forecast in the eastern Bay of Plenty, where flooding yesterday forced a family to evacuate, had caused no major problems overnight.
