Civil Defence is warning residents living near the Hikuwai River on the East Coast that evacuations may be likely overnight, while thousands remain without power in the upper North Island due to severe weather.
By late on Wednesday night, more than 190 millimetres of rain had fallen in areas north of Tolaga Bay over 18 hours, and more than 210 millimetres to the south-west.
Civil Defence controller for the Gisborne region, Peter Higgs, said the Hikuwai, north of Tolaga Bay, is expected to reach 10 metres overnight and, if it rises to 12 metres, evacuations are likely.
"The river's poised at quite a high level and if we do get a period of heavy rain tonight, then it will shoot up. The local residents are reasonably used to this and they'll just self-evacuate if it becomes necessary."
About a dozen roads remain closed in the district on Wednesday night.
State Highway 29 across the Kaimai Ranges is blocked by a large slip, about halfway to the summit on the Matamata side of the ranges.
Police said weather conditions are causing slips and flooding also on State Highway 36 areas in Western Bay of Plenty. Between 100 to 200 millimetres of rain is expected in parts of Tauranga and the remainder of the Western Bay over the next two days, with MetService warning of severe winds in some areas.
Bay of Plenty residents are also advised to watch out for surface flooding and rapidly rising rivers and streams, especially around high tide.
The New Zealand Transport Agency has lowered the speed limit to 50km/h in some areas as a safety precaution.
Driving remains treacherous in some parts of Coromandel, Waikato and Auckland in the aftermath of the storm. State Highway 25 was closed at Whitianga and Tairua and at Hikuai. Trees and power lines were down around parts of Morrinsville, Hamilton and Waingaro and a slip was causing problems on the road to Raglan.
Thousands still without power
Thousands of households in the upper North Island remained without power on Wednesday night after high winds hit overnight, toppling trees and damaging buildings.
Whangaparaoa, the North Shore, West Auckland and Great Barrier Island were hardest hit, with gale-force winds which littered the streets with debris.
Power company Vector said 9700 properties are without power on the Northern network, down from 40,000 on Wednesday morning. On the Auckland network, a handful of customers remain out, down from 6000.
A spokesperson said crews are continuing to work through the faults, but warns some of the outages are complex with several spans of lines damaged. He said the majority of properties should be reconnected within 12 to 24 hours, but some more complex smaller outages may take a little longer.
Great Barrier Island community board chair Izzy Fordham said there had been significant damage on the island, with landslides and damage to houses.
"We woke up to quite a bit of devastation. Typical storm damage - slips, trees (down), not too much in the way of property damage. One place lost its roof. A few of the generator sheds lost their roofs. The important thing is, of course, nobody was hurt or injured but it's certainly going to keep our contractors busy for a few days, that's for sure."
Lines company Vector spokesperson Sandy Hodge said two significant wind blasts hit about 11pm on Tuesday and 1am on Wednesday. One of its crews had a lucky escape when a large tree came down next to their truck, leaving it trapped.
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Auckland Civil Defence controller Clive Manley said it had received reports of damage to 147 buildings, with 25 sustaining significant damage
In the suburb of Herne Bay, two huge gum trees fell across the road. Wanganui Avenue resident Denise Cleverley said it was a miracle no one was hurt.
"If either of those trees had have fallen in a different direction it could have been a very, very tragic circumstance. Somebody could have got killed."
A child suffered minor injuries when a tree fell on a Whangaparaoa house - the only report of anyone hurt in the storm.
Wind strength had exceeded forecasts and more damage reports were likely to come in during the day, Mr Manley said.
The MetService said the biggest wind gusts in the region had been 145km/h an hour at Whangaparaoa and 170km/ at Tiritiri Matangi Island, just off the northern coast.
Animals at Auckland Zoo escaped harm from the storm, but repair work is under way there and the zoo was shut for the day. A eucalyptus tree up to 40 metres high fell and damaged part of the Pridelands area, where giraffes, zebras and rhinos are kept.