Heavy rain warnings are in place for Coromandel Peninsula, Bay of Plenty including Rotorua, Gisborne, Hawke's Bay, the Kaimai Ranges, the Tararua Ranges, and the Kaikōura Ranges.
Gisborne firefighters had a dozen calls overnight, most of them storm-related.
State Highway 2 between Gisborne and Opotiki is closed and about 16 local roads are also closed because of slips and flooding.
The closures have cut off the township of Te Karaka and residents are asked not to flush their toilets because of flooding overloading the sewage system.
Parts of the flood-damaged Tolaga Bay area could also be cut off, without power, for much of the day.
Gisborne Civil Defence manager Louise Bennett said staff would be monitoring river levels throughout the day.
"We need to take care of our neighbours, and check up on them, and just have that community spirit we are so well known for."
She said rural school buses have been advised not to run this morning. About eight schools and kindergartens are closed.
Police are also reporting slips on the Napier-Wairoa Rd and although a slip that blocked SH 5 at Te Pohue near Richmond Rd is now clear, the highway linking Napier and Taupo is soon to close because of multiple other slips and rain.
In Waikato a large slip is blocking the southbound lane of Thames Coast Rd near Whakatete and Ngārimu Bays.
Contractors are working to clear the slip but the road could be closed until midday.
Lines crews are dealing with power cuts across the island, including major outages in Taranaki, Rotorua and Hawke's Bay.
More than 5500 households and businesses throughout Kaiti and the whole of the East Coast lost power last night when a large macrocarpa tree fell across 50kV power lines in Valley Rd by the Massey Rd substation around 11pm.
Power is knocked out for 1570 Eastland Network customers after a trampoline blew into lines in the Te Araroa township. Crews are working to repair faults, but this will take time.
Power was also out in Tolaga Bay and Eastland Network said it would be off until at least later today.
Another 144 homes in Hastings and about 130 in Napier are without power, Unison said. Crews will start restoring power when it is safe to do so, the company said, warning locals they may be without power for "lengthy periods".
Bay of Plenty Civil Defence advised residents to secure structures like trampolines.
Rain watches are also in place in Northland south of the Bay of Islands, Auckland and Great Barrier Island, Waikato north of Hamilton, Taupō, Taihape, and the eastern hills of Wellington.
Air New Zealand has also advised that bad weather in the North Island may disrupt services today.
Eleven flights into Auckland Airport this morning were cancelled or delayed, and four flights from New Plymouth have been cancelled.
Also, watch out for strong winds in Bay of Plenty, Taupō, Taihape, Taranaki, Whanganui, Manawatu and Kāpiti-Horowhenua, and the Marlborough Sounds.
Gusts of up to 120km/h are forecast in these areas, which could damage trees, powerlines and unsecured structures. Driving may be hazardous, especially for high-sided vehicles and motorcycles.
Wind watches are also in place for Great Barrier Island, Auckland, Coromandel Peninsula, eastern Waikato, Gisborne, Taumarunui, Hawke's Bay, Nelson, Buller and Wellington.
A gust of 169km/h was recorded at White Island this morning but the strongest gusts are likely between 8am and 10am along southeast coastal Bay of Plenty and coastal areas from Gisborne to northern Hawke's Bay.
The Gisborne District Council said the city's wastewater network has again been flooded with large volumes of stormwater from residential properties.
To prevent sewage from overflowing back into homes and onto roads, causing a significant health risk, emergency sewer valves were opened.
MetService meteorologist Andrew James said the rain would ease in Northland, Auckland and Coromandel later today, but remain pretty wet and windy for most other places.
However, the South Island is looking a bit better, with cloud and a bit of rain and drizzle forecast in the east.
Heavy rainfall is forecast across the Kaikoura Coast this morning through to tomorrow. SH1 will likely be closed overnight tonight because of the increased likelihood of rock fall.
The road will open after it has been expected tomorrow.
Road users are advised to plan their journey and watch the weather or use the Lewis Pass route, which is clear from forecast snow over this period.
Tomorrow, there is a high chance of more heavy rain over Hawke's Bay, the Kaikoura Coast and coastal areas of north Canterbury, but the low should move away to the southeast on Thursday, bringing more settled weather.
Today's forecast
• Whangārei: A few showers gradually clearing. Westerlies. High 17C / Low 10C.
• Auckland: Periods of rain, possibly heavy, easing afternoon.
Strong southwesterly, gusting 90km/h, easing afternoon. High 16C / Low 12C.
• Tauranga: Periods of rain, heavy at times. Gale southeast turning gale northeast late morning, then northwest by evening. High 17C / Low 12C.
• Hamilton: Periods of rain, heavy at times. Strong southerlies turn westerly. High 16C / Low 11C.
• New Plymouth: Rain at times. Strong southeast, gusting 120km/h, easing evening. High 16C / Low 12C.
• Napier: Rain, possible thunderstorms until evening. Strong southeast gusting 100km/h, easing to northeast midday. High 17C / Low 13C.
• Wellington: Periods of rain, heavy at times. Gale southeasterlies gusting 100km/h, easing evening. High 13C / Low 11C.
• Nelson: Cloudy. A few spots of rain developing in the morning. Gusty southerlies. High 14C / Low 10C.
• Christchurch: Cloudy. A few spots of drizzle, turning to rain afternoon. Southerly breezes. High 10C / Low 7C.
• Dunedin: Cloudy with northeasterlies. High 10C / Low 8C.
