People are warned that heavy rain may cause streams and rivers to rise rapidly and surface flooding and slips could mean for hazardous driving conditions.
Heavy rain warning - orange
The weather authority's updated alerts show several main regions with a heavy rain orange warning in place.
They include the Coromandel Peninsula, Waikato, Bay of Plenty about and east of Whakatāne, Gisborne and Hawke's Bay north of Napier.
In the Coromandel Peninsula, the orange alert is in place from 9am to 5pm today; when periods of heavy rain are expected to bring between 40mm to 70mm.
Waikato's alert is in place until 5pm today. Between 40mm to 60mm is expected to accumulate there.
In Gisborne, locals are told to expect between 120mm to 170mm between 9am and 8pm today.
While in the Hawke's Bay, north of Napier, periods of heavy rain between 9am and 5pm today will see between 60mm to 100mm accumulating.
Heavy rain watches
Heavy rain watches will remain in place in the Bay of Plenty west of Whakatāne, including Rotorua, until 6pm.
Those in Westland, however, can expect a heavy rain watch for 27 hours from 6am on Wednesday to 9am the next day.
Locals are warned that rainfall amounts may approach "warning criteria" then.
Earlier today, a number of large-scale power outages were reported in parts of Auckland.
It comes as heavy rain is set to batter most of the North Island, including Auckland, as holidaymakers return from a long weekend away.
Authorities are dealing with outages in Auckland's Henderson Valley, Karekare, Huia and Piha.
Some residents have been without power since just after 10.30pm yesterday, according to Vector's website.
The outages in Henderson and Karekare were expected to be restored some time between 9am and 10am.
Vector said last night's wild weather had caused a number of outages around the city; with the biggest impact to people in Karekare, Huia, Torbay Heights and Parau.
"Vector crews are onsite at all locations as they continue to investigate and resolve faults to get the power back on for these customers as quickly and safely as possible," a statement said.
"(The) majority of customers in these areas are now back up and running."
Vector spokesman Marko Simunac said after the heavy rain watch was announced, more crews were organised to respond to outages throughout the night.
"We appreciate how frustrating it can be for our customers who are without power and would like to reassure them that (our) crews are working hard to assess the remaining outages and restore power as quickly as possible while it is safe to do so."
The outage in Huia was reported about 7.30am today. Some homes appear to have had electricity restored.
The circumstances of the outages are not yet known.
Those affected in Piha can expect to have power back between 9am and 10am.
"There are a variety of reasons why outages happen," the website says.
Fire and Emergency NZ have been kept busy overnight; with 27 weather-related call-outs in the Auckland, Waikato and Northland regions.
All the incidents were related to trees coming down or flooding.
However, they were all considered to be minor incidents and there were no reports of injuries or evacuations, a northern fire communications spokesman said.
A total of 10 incidents were reported around Auckland; 13 in Waikato and four in Northland.
Fire crews were also called to reports of a tree falling and blocking a road in the Bay of Plenty about 6.15am.
Firefighters used a chainsaw to cut the tree and remove it from the road, FENZ said.
Last night, MetService issued a number of new heavy rain watches and orange warnings for the North Island.
Auckland MetService has issued a heavy rain warning for Auckland through to at least midday on Monday. The region has been experiencing wet, humid conditions.
Meanwhile, heavy rain watches have also been issued for Bay of Plenty, Great Barrier Island, Hawke's Bay and Rotorua.
Earlier on Sunday, heavy rain battered the Taranaki region on Waitangi Day, with one weather station recording a month's worth of rain in just four hours.
The rainfall, which followed flooding on the South Island's West Coast earlier in the week, has closed roads, downed trees and caused slips.
MetService issued a "red" weather warning in place for the region, and on Sunday afternoon reported 138mm of rain had been recorded at Cape Egmont between 6am and 10am.
"This is truly exceptional rainfall for a station at sea level," MetService said on Twitter.
"For some perspective, this is the same amount of rainfall that New Plymouth would experience in a typical July across the entire month."
Rain around the coast and in South Taranaki was subsiding but flooding was still present at about 5pm, Taranaki Civil Defence Emergency Management said in a Facebook update.
Just after 10pm it was announced that SH1 Marton, between Wings Line and Calico Line, was closed because of flooding.
Detours were in place.
State Highway 45 between Pungarehu and Warea is closed at the intersection with Newall Road because of flooding.
Saddle Rd, northeast of Palmerston North, between Ashhurst and Woodville, is closed overnight, following slips earlier on Sunday.
Motorists are asked to avoid travel, or take a different route such as the Pahiatua Track.
Many roads in the region are blocked or disrupted with slips, debris and surface flooding and the South Taranaki District Council is urging the public to avoid driving if possible, and take extreme care if travelling.
Footage filmed by residents in Rahotu, 50km south of New Plymouth, showed fast-moving water racing down a flooded street.
One resident said the town hall had flooded and sewage and fuel could be smelt in the streets.
Taranaki Civil Defence said that while MetService's weather warning was being lifted at 2pm, heavy rain was continuing this afternoon.
It said State Highway 45 between Okato and Opunake remained closed, and a detour was in place. Motorists were advised only to travel if necessary, and not to drive through floodwaters.
Civil Defence also said it had received reports of slips on SH3 at Mount Messenger and south of Hawera, though these roads remained open.
Rivers were flowing at high levels and people in the region were warned to keep away.
There are also heavy rain warnings in place for the Hawke's Bay north of Napier and Gisborne and the Tararua Ranges.
More rain is expected this week particularly in the flood-hit West Coast of the South Island. MetService is forecasting another active front bringing rain to Westland, Buller, Tasman west of Motueka and the Nelson Lakes late Wednesday and Thursday.
People are advised to stay up to date with the latest forecasts and advisories.
