A state of emergency was declared in Paekakariki after a flash flood ripped through the town on Friday night.
Slips closed roads in and out of the town, stranding 200 commuters and causing havoc with traffic heading out of Wellington.
Devastation hit disbelieving locals returning to their homes on Saturday morning.
"I opened the window and the water was at the window level, I just had to get out and swim...I can't believe it," says evacuated resident Itiria Debreceny.
A surf club dinghy rescued her family.
"Within about five minutes the water rose up about a metre - our furniture, our fridge, all went floating past us," she and her husband Craig say.
The storm hit hard around 9:30 on Friday night.
Cancelled trains stranded hundreds of sodden rugby fans heading north after the Wellington-Otago game.
Some slept in the stadium, while others joined a frustrated queue going nowhere.
In Paekakariki a massive slip rumbled down the hill, blocking State Highway One and burying the local motel and any cars in its path.
Transport in and out of Paekakariki was at a standstill with cars submerged.
The state of emergency would be in place until at least midnight on Saturday.
Drinking water was scarce as the intake was damaged during the storm, and power was shut down to all flooded buildings.
The cleanup was continuing for local businesses and the 12 families evacuated.
18 Paekakariki residents will be out of their homes on Saturday night, due to flooding.
The Kapiti civil defence controller Roger McCormack says most are being put up with family and friends and four had to stay at the local backpackers.
Road and rail chaos
Police were urging people to avoid the area around Paekakariki througout Saturday and State Highway 1 between Paramata and Paraparaumu was closed for several hours on Saturday, and queues stretched for about six kilometres at one stage when it was re-opened.
Southbound traffic into Paekakariki was expected to be down to one lane until early on Sunday morning.
Akararawa Road and Paekakariki Hill Road remained closed early on Saturday evening.
A rail passenger service is operating between Wellington and Paekakariki despite one of the two lines being out of action.
Extreme caution has been urged on the Rimutaka Hill Road.
The bad weather has also left its mark on the far south with cold temperatures and snow killing many hundreds of lambs.
Trucks laden with dead lambs were a common sight on rural roads in South Otago on Saturday.
One was expecting to collect more than a thousand carcasses before the end of the day.
Elderly man drowns
Rough seas have also led to the death of an elderly man off the Kaikoura coast.
The man drowned after his four metre runabout fishing boat was flipped by the freak wave off Baxters Reef.
He had been fishing with a friend when the wave hit and the two were not wearing life jackets. They were plucked from the water by the crew of another fishing boat.