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Fire service northern communications said this morning they had had more than 100 flood-related callouts overnight in the Whakatane area.
Fire services had helped residents in flooded homes where they could and the situation settled by dawn, a spokesman said.
The rapidly rising floodwaters last night forced Bay of Plenty residents from their homes and trapped motorists - including an elderly woman who had to be pulled from her partially submerged vehicle.
Torrential rain in the upper North Island yesterday left sodden homes, flooded farmland and swollen rivers threatening to burst their banks.
Late last night the downpours were moving east of Whakatane and Matata, where roads were closed by flooding and slips, trapping several motorists in their cars.
In Whakatane, the local council's emergency operating centre was activated late in the day after 124mm of rain which fell during two hours, flooding homes and streets.
Controller David Bewley said a welfare centre had been opened in the town's War Memorial Hall for residents forced from their homes.
Fifty people were staying there by 9.30pm.
Whakatane resident Jackie Bettelheim had to take quick action to protect her home against fast-rising floodwaters.
"We got all the sheets and towels out of the cupboards to make barriers to stop it coming in," she said
Fortunately the water stopped rising as it lapped the top step to her front door.
Fire Communications Centre shift manager Jaron Phillips said firefighters were kept busy dealing with the effects of the storm.
In Matata, two women, one of them elderly, were trapped in their car under a bridge by rising water for about 20 minutes.
"They were certainly panicking. They went under the bridge and the water was too much for them and they got stuck."
It is believed firefighters waded out to rescue the women from their partially submerged car.
The elder woman was treated for hypothermia and taken to hospital.
At the Police Northern Communications Centre, Inspector Ian Brooker said flooding was widespread along the East coast of the Bay of Plenty, from Ohope to Whakatane.
State Highway Two was impassable in several places because of flooding, slips and debris.
"Contractors are out right along the coast and some sections of road have been cleared by locals using tractors," Mr Brooker said.
"Several people have had to be rescued from vehicles stalled in floodwater."
Earlier in the day the Coromandel Peninsula was hit by heavy rainstorms, and one school sent children home early.
Roading contractors reported slips on SH25, and farmers south of Tairua moved stock to higher ground.
Tairua couple Lou and Robyn Mackwell were last night waiting anxiously for the rising tide to decide whether they would have to evacuate their Ocean Beach Rd home which was surrounded by rising floodwaters.
The normally placid stream running through their backyard had risen more than 2m and was almost lapping the back door of their small home.
"We are just waiting to see what the high tide will do ... if it continues to rain hard we could be in the poo."
In Whitianga firefighters pumped water from eight homes and helped some residents lift furniture to higher ground.
In Auckland, firefighters were kept busy by calls to flooding in homes, shops and an industrial park.
One call came after a rising river spilt into the empty basement of a building on Great South Rd, Penrose, causing up to a metre of flooding.
Metservice lead forecaster Mark Schwarz said that at the peak of yesterday's storm, 90mm of rain fell on Whakatane in one hour, followed by another 34mm in the next hour - levels seen in tropical thunderstorms.
"Those are big numbers - it's not setting a New Zealand record, but it's getting there," he said.
Up to 30mm an hour of rain fell on the Coromandel, and up to 20mm an hour hit the Far North and Auckland.
Mr Schwarz said the worst of the bad weather appeared to now be over but people in the upper North Island could still expect some unsettled periods today, with showers and some thunderstorms.
The rain was not expected to be anywhere as heavy as yesterday, but the fact it was falling in already sodden areas could cause some problems.
Mr Schwarz said the weather was caused by several fronts which were spiralling a low in the Tasman Sea.
The Metservice said the heavy rain should ease by early morning today.
The service reported clear skies in Whakatane at 7.45am.
- ADDITIONAL REPORING: JAMES IHAKA, MICHAEL DICKISON