Rising rivers have caused State Highway 2 to be closed overnight between Napier and Wairoa.
The highway flooded near the small settlement of Turiroa, 5km west of Wairoa, and has been closed at Whirinaki near Napier and at the Wairoa township at the intersection of State Highway 2 and Mitchell Rd.
Police said motorists should delay all travel on the highway overnight.
The road will be reassessed in the morning, police said.
Meanwhile, a township isolated after widespread flooding looks unlikely to be evacuated as the water levels subside.
Torrential rain struck Gisborne region overnight and through the day, with 114mm of rain recorded at Gisborne Airport in the 24 hours to noon.
Gisborne Civil Defence said at 11am that evacuations were being considered for residents of the settlement.
At 2pm, Chief Fire Officer for Te Karaka Rural Fire Brigade Jamie Simpson said the rainfall had subsided.
"There's a fair bit of flooding around, and we're isolated now, the road is closed at both ends," he said.
Evacuations were still possible, but unlikely he said.
"The rainfall has subsided and the river is slowing down... it hasn't peaked, but the rate it's rising has slowed down."
Mr Simpson said no properties were in danger, but a lot of farmland was swamped.
Federated Farmers provincial president Sandra Faulkner says it's a bad time to get so much rain at once because it could cut production from lambing.
Wairoa resident Rangi Burrows said the Wairoa River was looking as high as it was during Cyclone Bola.Mr Burrows property is right on the river bank and said the flow of the river was very fast.
"As soon as the open the bar up and let the river out we'll be right," he said.
"I live on a small farm... I've got no animals to worry about it."
Earlier today a man had to escape from his car when it became overcome by floodwater in Rototahi, south of Tolaga Bay.
Civil Defence has sand-bagged was in progress for one Graham Rd resident in Kaiti.
Wairoa District Council had closed 18 roads in the region due to flooding, slips, and debris from downed trees.
Patunamu Rd was impassable from debris from a forestry site being carried onto the road.
Large slips had also caused problems in various parts of Wairoa.
MetService meteorologist Tom Adams said the rainfall was "a rare event".
"Most of the rain is falling up in the hills [of the Gisborne and Hawkes Bay regions] and we have a whole bunch of stations recording well over 150mm [in the last 24 hours]."
Two stations in the hills around northern Hawkes Bay had recorded over 170mm, Mr Adams said.
Mr Adams said the rain was expected to continue to fall heavily until tonight, including some localised bursts of heavy rain and hail in the region.
"There's also some reasonable thunderstorm activity expected, especially north of Mahia," he said.
As the focus of the rain moves south, Wairarapa can expect periods of heavy rain from late this afternoon until Thursday.
Marlborough and the Kaikoura Coast look set for an extended rainy spell between tonight and Thursday.
Further south, Canterbury can expect a good dose of rain from Tuesday, and eastern Otago from Wednesday into Friday.
"There is some good news amongst that, a lot of those areas really need that rain. So while there is annoyance for commuters in the main centres there is relief for farmers," Mr Adams said.
The Hikuwai River was rising by a metre an hour this morning, but was stable north of Tolaga Bay at 8m and may have peaked.
The Waimata River gauge at Goodwins reached 8.8m by mid-morning.
Gisborne's river is now flooding ....Not a good day for one's washing ....... #nz #lovegisborne pic.twitter.com/N9uY8QgBMs
— André Hock (@transparency_a1) September 20, 2015
SH35 is flooded between Tolaga Bay and Tokomaru Bay and the New Zealand Transport Agency has issued a warning for flooding at Okitu.
SH2 is closed from Opotiki to Gisborne because of flooding at Te Karaka.Tolaga Bay Area School and Te Karaka School are closed and Gisborne Civil Defence spokeswoman Sheridan Gundry said there was surface flooding across the district and a number of trees were down on roads.
The council said manholes had over-topped in Gisborne and sewage valves have been opened to relieve pressure and prevent sewage flowing into properties.
In Waikato, a slip blocked the road to Aotea in the Otorohanga district this morning, but Otorohanga District Council hoped to clear the road before lunchtime.
Snow and sleet is expected to fall in parts of the Central Plateau and Taupo this afternoon.
MetService is forecasting sleet and possible snow about the summit of the Napier-Taupo Road until 6pm today.
Up to 2cm could fall above 700m.
Snow was also expected on higher parts of the Desert Road this afternoon.
One flight from Gisborne Airport has been cancelled because of the rain.
The flight to Wellington had been scheduled to depart at 12.30pm.
NZTA has warned Wellington motorists, pedestrians and cyclists to keep their wits about them and take extra care as the weather battering Gisborne and Hawkes Bay moves into the region.
The weather was reported to have contributed to a number of crashes this morning, so motorists were advised to take extra care on their trip home this evening.
Regional performance manager Mark Owen said winds would get stronger and rain heavier this afternoon.
In Waikato, a slip has blocked the road to Aotea in the Otorohanga district this morning.
Waikato Civil Defence shared a photo of the slip on Twitter and said Otorohanga District Council hoped to clear the road before lunchtime.
Here is the big as slip going to Aotea-the road is shut-Oto DC hope to open the road by lunch today #DriveLikeANana pic.twitter.com/fmJtBztGby
— Waikato CivilDefence (@CivilDefenceWKT) September 20, 2015
MetService meteorologist Tom Adams said the rainfall was "a rare event".
"Most of the rain is falling up in the hills [of the Gisborne and Hawkes Bay regions] and we have a whole bunch of stations recording well over 150mm [in the last 24 hours]."
Two stations in the hills around northern Hawkes Bay had recorded over 170mm, Mr Adams said.
The river is up, a perfect morning to imagine I'm a captain - surveying the Taruheru from #thestarofcanada #gisborne pic.twitter.com/N2eQx4BwmR
— Tairāwhiti Museum (@Tairawhiti_muse) September 20, 2015
"Gisborne Airport has recorded 99mm in the last 24 hours, and to give that some context their monthly average for September is 66mm."
Mr Adams said the rain was expected to continue to fall heavily until tonight, including some localised bursts of heavy rain and hail in the region.
"There's also some reasonable thunderstorm activity expected, especially north of Mahia," he said.
Tonight the rain band will be tracking south, and MetService has issued heavy rain watches for Wairarapa and Marlborough.
Mr Adams said the rain could be heavy, but there was less certainty around how much rain could be expected.
The heavy rain would make its way south to Canterbury and Otago on Wednesday.
"There is some good news amongst that, a lot of those areas really need that rain. So while there is annoyance for commuters in the main centres there is relief for farmers," Mr Adams said.
One flight from Gisborne Airport has been cancelled because of the rain. The flight to Wellington had been scheduled to depart at 12.30pm.
NZTA has warned Wellington motorists, pedestrians and cyclists to keep their wits about them and take extra care as the weather battering Gisborne and Hawkes Bay moves into the region.
The weather was reported to have contributed to a number of crashes this morning, so motorists were advised to take extra care on their trip home this evening.
Regional performance manager Mark Owen said winds would get stronger and rain heavier this afternoon.
"Bad weather makes the roads more dangerous. Heavy rain makes our roads more greasy, and reduces visibility - this adds up to a greater risk of crashes.
"To adjust for the weather, it's important to drop your speeds, increase your following distances, and drive to the conditions."
Mr Owen said it was not only drivers who make errors in wet weather.
"When it's hosing down, pedestrians sometimes make rash decisions when crossing the road. Raincoat hoods can also impede visibility, and we're asking motorists to keep their eyes peeled for pedestrians and expect the unexpected."
Mr Owen said motorists should also be on the lookout for surface flooding, slips and debris brought down by the rainfall.
Travel on the Rimutaka Hill Road, SH2, or on the Kapiti Coast will be difficult for high sided vehicles like caravans, trucks and campervans as well as for motorbikes due to high winds.
MetService has warned up to 10mm of rain is forecast for this evening in Wellington with more coming overnight.Southerly gales may become severe in exposed places of Wellington and the Kapiti Coast until tomorrow morning.
A storm warning is in place for the Cook Straight with southerlies expected to reach 100km/h and a 4 m swell
Snow and sleet is expected to fall in parts of the Central Plateau and Taupo this afternoon.
MetService is forecasting sleet and possible snow about the summit of the Napier-Taupo Road until 6pm today. Up to 2cm could fall above 700m.Snow was also expected on higher parts of the Desert Road this afternoon.
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