Driving conditions were hazardous, with many slips across the North Island and a lot of surface water, said Sergeant Andy Dow, from the police central communications centre.
Motorists were advised to take extra caution on State Highway 2 between Napier and Wairoa, SH 3 from Wanganui to Taranaki, SH4 from Wanganui to Raetihi and SH5 from Napier to Taupo due to minor slips and surface water on roads.
There were also reports of flooding and a vehicle crash due to wet roads on State Highway 1 north of Waiouru, and the Desert Road between Waiouru and Turangi had closed.
Surging tide waters flooded the Auckland city-bound lanes of the Northwestern Motorway (SH16) across the Waitemata Harbour, closing lanes for 4-1/2 hours on Sunday afternoon, with drivers diverted on to arterial roads.
A combination of strong winds, rain and flood-swollen rivers, together with more extreme high tides, would make driving conditions dangerous, New Zealand Transport Agency state highways manager for Auckland and Northland Tommy Parker said.
A southbound section of the Northern Motorway (SH1) near the Auckland Harbour Bridge was also closed by tidal flooding for about an hour this afternoon. The storm also affected communication links to some electronic message boards on the motorway network, and there were slips on the Brynderwyns on SH1 and flooding near Paihia on SH11 in Northland.
About 300 people were evacuated from a Taupo campground this morning as Waikato authorities prepared for flooding across the region.
Campers were asked to leave the low-lying Spa Park, and people living close to rivers and lakes were told to prepare for rising levels over the next three days.
The Fire Service responded to more than 100 weather-related events this morning in the northern region, but heavy rain had eased in Auckland and Northland by early afternoon.
The worst-affected areas were Auckland's North Shore, eastern suburbs and the lower central business district, Fire Service northern shift manager Jaron Phillips said.
Homes had flooded across the Auckland region, and many commercial premises in central Auckland had flooded due to the high tide.
The Fire Service is also keeping a close watch on increasing numbers of incidents in Rotorua and Edgecumbe.
In downtown Auckland, flooding closed Quay Street between Britomart Place and Tinely Street earlier today.
A car collided with a fallen tree in the Waikato just after 6am, in what was not a serious crash but closed Maungatautari Road.
Further south, weather had forced the cancellation of the flying programme at Wings Over Wairarapa.
Senior Sergeant Marty Edgehill, of police central communications, said there had been slips, debris on the road and minor crashes in the central and lower North Island.
"It's quite noticeable that were having a fair bit of activity that can be put down to the weather," Mr Edgehill told NZPA.
The MetService had issued a severe weather warning for most of the North Island, including the Bay of Plenty, and Civil Defence authorities were on alert.
A revised forecast was issued just before noon predicting much less rain than expected would fall today, after an unusual tropical air mass pushed across Auckland this morning. That caused temperatures to jump 6degC in just 30 minutes, and humidity rocketed to 100 percent.
Rain had eased in Northland and Auckland, and was likely to ease in Coromandel Peninsula by early afternoon.
For Northland and Auckland, occasional rain with a few heavy falls was likely for the remainder of the day, with another 20 to 40mm possible.
Another 20 to 40mm rainfall was possible north of Whitianga, while 40 to 70mm was likely further south.
