Severe winds and heavy rain have ripped through parts of the north, with reports of damaged buildings and power cuts flooding in, said police.
Seventy-six flights have been cancelled and the ports of Wellington, Rotorua and Wanganui have also been affected by the adverse weather.
The deepening low was expected to move down the island towards the Wairarapa and "hitting the areas in-between," said Metservice meteorologist Daniel Corbett.
"It will be shifting across the lower north. It's still going to be very strong to severe gales, especially in the Wairarapa coast and Hawkes Bay over the next eight hours," he said.
"It will be heavy persistent rain, sodden ground and the rain and wind are making it really mucky for travelling."
It had been "a few years" since such a a deep low had been felt in some of the worst-hit areas, said Mr Corbett.
The weather bomb, an 'explosive cyclogenesis', was defined by a deepening low that quickly strengthened and intensified, he said.
In Auckland winds were expected to increase to 100-kph this afternoon.
Earlier today, gusty winds pulled a large tree from its roots causing it to crash over a fence and into a neighbouring property in Henderson.
Zia Ahmad's family felt frightened as wind howled through their house before a loud "cracking" noise came from outside about 9am.
He said the neighbour's tree had crashed over the fence and into their backyard, narrowly missing the house in Hinerau St.
"My wife was scared," Ahmad said. "We are lucky there was no damage and it didn't fall on top of the house because I have a baby and he was sleeping at the time."
The 34-year-old said his family - including his parents who also lived at the house - had been on edge during the night as the house shook and trees were on the verge of crashing down.
Ahmad said he was yet to talk to his neighbour but the fire service had been around to chop down branches, creating a clear pathway around the house.
Downed power lines cause a four-hour power cut to Waitakere's Karekare.
In the small Taranaki settlement of Patea 50 houses lost their roofs, shop fronts were ripped away, windows blown out and trees toppled "everywhere" early this morning, said the town's fire chief.
Patea Volunteer Fire Brigade chief fire officer Grant Hurley said emergency calls began flooding in about 5am as the "quick and nasty" storm made its presence felt.
Firefighters focused on making sure people were safe, with dozens of residents seeking safety in the fire station, and did not go onto roofs during the storm. He was not aware of any injuries.
Power went out about 6am and remained cut at 11am.
There was no epicentre of damage, he said.
"Everywhere was hit."
Kelly Dwyer, who lives in Stafford St, said a power pole fell onto a boat outside her aunt's house across the road, but no one was injured.
The storm was frightening, Dwyer said.
"It was shaking the whole house."
Longtime Norfolk St resident Lina Baldwin said the storm was the worst she had experienced since moving to Patea in 1959.
"The wind, gee whizz, the house was shaking. I kept on putting my head under the blankets."
John Newton drove from Waverley to Patea this morning and said he had to dodge flying debris.
"Sheets of roofing iron were hurtling down the street. I couldn't drive up the street. The iron was flying at car height and over the car," he said.
He said he took the side streets in Patea to avoid the flying roofing iron but ran over power lines that had come down.
Trees and debris littered a 100m stretch of State Highway 3 near Manawapou Hill this morning, causing "very, very hazardous driving conditions", said Inspector Paul Jeremy.
Fire central communications shift manager David Miekle said teams in Southern Taranaki, from Manaia through to Wanganui, were working flat out to help those in trouble.
He said the reports of roofs being blown off were continuing to grow, along with power cuts and fallen power lines.
The storm is also being felt in Wellington, where trees have fallen on Wainuiomata Road and Ngaio Gorge Road.
A driver crashed into the tree on Wainuiomata Road, but escaped uninjured.
Police are urging to motorists to avoid travelling if possible, as emergency services tend to the overwhelming number of people needing help.
