Hundreds of people are without power, schools and roads are closed, and people have been advised to consider evacuating as ongoing heavy rain lashes the upper North Island.
Parts of Northland have already copped more than 200mm of rain - with the worst of the storm expected to come tonight.
As of 8am today, Weta, on the east coast near Whangaroa Harbour, had recorded 221mm in the previous 24 hours, while Kerikeri had recorded 200.5mm.
State Highway 1 is blocked at Mangamuka, south of Kaitāia, by flooding, and warnings of surface flooding are in place on many other roads.
SH1 is the main connection to Kaitāia but is prone to flooding and slips.
Fire and Emergency New Zealand (Fenz) was earlier urging residents in storm-affected areas to be ready to evacuate if necessary.
A red weather warning remains in place for Northland east of Kaikohe from Doubtless Bay to Whangārei, with the worst of the downpours expected to hit on Thursday afternoon.
Marae in the region have been opened for those in need of support, and Fenz has deployed 19 specialist rescue personnel to Northland and Auckland.
As many as 5000 consumers were without power at one stage overnight, but that number had dropped to several hundred by 9am.
MetService said the heaviest rain and largest volumes were likely to be in the upper North Island, from Northland to western Bay of Plenty.
Downpours, flooding, and slips were also possible on Thursday and Friday.
Fenz assistant national commander Ken Cooper warned residents in upper parts of Northland to be ready in case the situation deteriorated.
"For that upper part of Northland, the intelligence we've got is there's a large amount of rainfall over a very short period of time. I would certainly advise people to be prepared, if they're in low lying areas or near rivers, be prepared to move."
Cooper said anyone concerned about a risk to life or property should call 111.
Northland Civil Defence expected the worst of the rain to hit the northeast coast on Thursday night.
In a post on social media, it warned residents not to go into flood water, to avoid unnecessary travel, and to be aware of slips.
"Leave immediately if you notice cracks in the ground, leaning trees or power poles, unusual sounds, or sudden changes in streams," it said.
Whangārei Mayor Ken Couper told Morning Report it had been a wild night with strong winds and consistent but not heavy rain in Waipu, just south of Whangārei.
It was too early to say whether the situation was different up the coast, he said.
"We are concerned because of the weather event that we had in January and the fact we're still recovering from that."
Power was out last night in Oakura, which was affected in the last storm, he said.
All of the 200 slips except for a massive one had been cleared after the January event, he said.
"But there's a number of sites where we were hoping for more time to pass to get things more stable before rain came."
