Transport authorities have urged motorists to avoid unnecessary travel in Waikato and Bay of Plenty as forecasters warn heavy rain is likely to cause more flash flooding and slips.
Heavy downpours eased during the middle of the day before a second band of torrential rain returned to eastern Coromandel and western Bay of Plenty this afternoon.
Authorities in Waikato and Coromandel are continuing to monitor river levels and have warned farmers to move stock to higher ground if necessary.
WeatherWatch forecasters said the rain could linger until early evening, making further flash flooding and slips highly likely. Power cuts may also occur due to slips.
Conditions were expected to ease this evening, but further heavy showers were possible overnight and to a lesser degree tomorrow.
The heavy rain today forced the closure of some roads and state highways in Coromandel, Waikato and Bay of Plenty.
New Zealand Transport Agency (NZTA) acting state highway manager Karen Boyt said the agency was closely monitoring all roads in the area as the rain continued to fall.
"Slips are also likely to occur with this quantity of rain falling and motorists should consider avoiding travel tonight in the Waikato and Bay of Plenty if at all possible," she said.
"If drivers must travel we urge that they take extreme care on the highways, drive to the conditions, and allow more time for their journeys so that they can reach their destinations safely."
The road between Tauranga and Waihi has reopened to one lane after a slip closed State Highway 2 at Athenree Gorge, 48km northwest of Tauranga, for most of the afternoon.
The NZTA said the road would remain open overnight, but motorists have been warned to expect delays.
Work crews would begin clearing the slip tomorrow.
SH2 remains closed between Waihi and Paeroa due to rising Ohinemuri River levels through the Karangahake Gorge.
Surface flooding and potholes have also formed on SH2 between Bruce Rd and the Domain Rd intersection in areas that were resealed late last week.
The road between Morrinsville and Paeroa, SH26, is closed at the Criterion Bridge in Paeroa after the Waikato Regional Council closed the floodgates on the rising Ohinemuri River.
High tide was due about 10pm, which was likely to lead to further bridge closures.
Authorities were monitoring river levels at the Waihou River on SH2, north of Paeroa, and the Tairua River on SH25 at Hikuai.
The NZTA said the Waioeka George, Waimana Gorge and Wainui intersection in eastern Bay of Plenty could be affected as the weather moves east.
The Thames Coromandel District Council is monitoring flooding after up to 200mm of rain has fallen over the past day.
It said the fords at Kauaeranga Valley Rd, Old Maratoto Rd and Wires Rd were impassable due to flooding.
Flooding had closed Wentworth Valley Rd, School Rd, and Settlement Rd, while the Tapu-Coroglen Rd was down to one lane in places due to slips.
"If you see signs warning you not to drive into certain areas due to flooding, please take the advice. Last year, too many people tried and failed and turned their motorhomes and other vehicles into temporary submarines," the council said.
Waikato Regional Council duty emergency management officer Greg Ryan said the Ohinemuri River was in flood and the Piako, Waihou and Waitoa rivers were expected to become swollen over coming days.
Further west, the rain was expected to prolong flooding of the Waikato and Waipa rivers, which rose after heavy rains the weekend before last.
Farmers in Coromandel and Waikato have been advised to move stock to higher ground if necessary, and all residents were urged to stay up to date on river levels.
Both regional councils said there was potential for flood plains to be inundated, causing general surface flooding and disruption to transport around the region.
Authorities were keeping in touch with other agencies over any flood response.
"It looks as though we're in for a few very wet days on top of what has already been a very wet July, so risks will certainly be elevated this week," Mr Ryan said.
In Bay of Plenty, rescuers braved high winds and driving rain to fly a pig hunter out of the Lake Rotomahana area.
The 42-year-old Rerewhakaaitu man was reported missing after becoming separated from his hunting party in heavy rain yesterday.
Police searchers found him, suffering from hypothermia, in an area above bluffs at 10.15am today.
He was evacuated by helicopter and was recovering in Rotorua Hospital.
"This was particularly challenging as the weather conditions were dreadful, with winds and driving rain, and the location of the hunter on the mountain was just below the cloud base," police said.
WeatherWatch said the large sub-tropical low bringing the wet weather would cross the upper North Island over the next day or two as it slowly fizzled out.
The low would be followed by a large high that would bring sunnier and drier weather across New Zealand, with conditions improving in most places on Wednesday and Thursday.
WeatherWatch said the weather would mostly be settled by Thursday through to Saturday.
There could be some showers around East Cape, Gisborne and Hawkes Bay on Thursday, possibly lingering around Gisborne on Friday, and light rain and showers on the South Island's east coast on Tuesday and Wednesday.
Rain was expected to turn to snow above 500m around Christchurch on Wednesday, with sunnier weather returning on Thursday.
Temperatures in the North Island were expected to remain above average for the rest of July.