MetService yesterday issued a rare red wind warning - its highest - as winds of up to 150km/h were recorded, saying there was "threat to life".
Severe winds smashed Wellington, lifting roofs, felling trees, closing roads and sparking numerous emergency callouts.
Power has been cut to thousands of properties across Wellington, Wairarapa and Manawatū.
Wellington is under an orange level heavy rain warning until midday, and Wairarapa, south of Masterton, until 3pm.
Wellington Region Emergency Management Office said people should expect to see debris and some surface flooding on the roads.
"We are still advising people not to travel unless necessary. If you do need to travel, plan ahead, drive to the conditions, be aware of debris and expect delays."
A Lower Hutt woman who had a narrow escape from a falling branch as the wild winds ripped through Wellington is calling on the council to chop back two pohutukawa trees heavily.
Julie Paterson was on Hayward Terrace, in the suburb of Waiwhetū, when she heard a loud crack and ran for her life as a branch fell towards her yesterday. She said it was terrifying and the city council needed to do something about it.
More disruptions as flights resume
Wellington Airport advised that conditions had eased enough in the capital for flights to begin operating again.
However, the airport is cautioning that there still may be some disruptions today, depending on the weather. Passengers should check with their airline for specific flight information.
A number of passengers had to sleep at the airport overnight due to cancelled flights and full hotels.
Some 200 flights were cancelled in and out of the capital yesterday, and there had been a couple of cancellations and diversions this morning.
Wellington Airport's head of operations Matthew Palliser told RNZ's Nine to Noon programme today they are operating in recovery mode to clear the backlog.
He said some people slept in the airport last night. "Our hotel was full and we had a number of people who had to stay in the terminal, so we kept the heating on and looked after them."
Palliser said that number of flight cancellations was rare - even for a normally windy Wellington.
"It's highly unusual to have to cancel the flights for an entire day. We do have periods sometimes where flights are diverted because of winds, but to have a whole day was definitely an exceptional circumstance.
"If passengers can make sure they are communicating and checking with their airlines that flights are on time, and make sure you come to the airport nice and early as there will be high volumes of people coming through."
Interislander Cook Strait ferry sailings have been cancelled until at least this afternoon due to big swells, while Bluebridge sailings won't resume until tomorrow.
Roads affected
Roads on Wellington's south coast remain closed because of debris thrown across them by big seas yesterday.
The city council said it was likely sections of the road from Seatoun to Ōwhiro Bay would be closed for much of today while crews check on damage and start a clean-up. The stretch between Lyall Bay and Island Bay is open.
Hutt City Council said it remained in an active emergency response and contractors have been out across Lower Hutt overnight clearing debris, unblocking drains and addressing hazards.
The Lower Hutt suburb of Eastbourne remains cut off this morning.
A slip on Ferry Rd in Days Bay is blocking both lanes with no access in or out, apart from emergency vehicles.
Hutt City Council said contractors plan to open one lane for residents.
Both lanes of Wainuiomata Hill Rd would be opened for peak traffic travelling to Lower Hutt this morning, though lanes may be reduced at 10am to pull down potentially loose material and mitigate further slippage, which may take a number of hours.
The Petone Esplanade around the Cuba St area is experiencing significant surface flooding and people have been told to avoid the area.
