About 280mm of torrential rain fell in the eastern hill country of Northland over 12-14 hours from 1pm on Friday, causing substantial damage to the region's road network and some water and sewage treatment plants.
River levels have begun to drop but the areas worst affected are along Northland's east coast from Kaitaia in the north to Mangawhai in the south.
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Paihia's water treatment plant was also damaged and residents are being asked to conserve water over the next 24 hours.
There are also power outages at Taupo Bay, Kaeo, Matawaia and Hihi.
Bay of Plenty Regional Council rivers and drainage staff are also busy responding to flooding-related calls including over-flowing drains, streams and canals.
Police were being inundated with calls about slips, road closures, trees over roads and surface flooding from Maunganui to Warkworth, police northern communications shift commander Shawn Rutene said.
The severe weather was moving towards Tauranga, Whakatane and Awakeri, and the bridge between Tauranga and Mt Maunganui was closed.
People in Rotorua were also being urged to stay at home and only travel if necessary, as flood waters are blocking a number of roads around the city centre.
The MetService said Wilma should pass just to the north of East Cape late on Saturday morning before racing away to the southeast.
