Cyclone Gabrielle is bringing a 'dangerous combination of high winds and heavy rain' today, says Minister for Emergency Management Kieran McAnulty.
McAnulty says the impacts of Gabrielle are now being seen with heavy rain and severe wind in the upper North Island including with damaged roads, downed trees and power outages.
"MetService has advised me that today is the critical day in the event.
"Please keep up to date with MetService for weather warnings, and your local Civil Defence Emergency Management group for local updates."
He says the need to declare a national state of emergency is being monitored and actively reviewed every four hours.
"We have not reached that point and we may not have to. This is an all of government response with all agencies ready to respond as needed."
A state of emergency has been declared in Northland, Auckland, Thames-Coromandel and this morning Ōpōtiki and Tairāwhiti.
McAnulty says the key question at this point guiding the decision to announce a national state of emergency is whether local civil defence agencies are able to respond to their local needs.
"We would take advice from them as to how they're coping."
He says there have only been two national states of emergency in New Zealand's history - the Christchurch earthquake and Covid-19.
"We don't need a national declaration to assist them ... what it means is that National Emergency Management Agency (NEMA) would be able to in some instances take control and intervene in certain aspects of it."
He says the lines agencies have given an assurance people will be reconnected as soon as possible but with the weather still having an effect, "it's actually unsafe for them to do so right now".
Some farmers might have to make some tough decisions around milk and that sort of thing, he says.
McAnulty acknowledges the work of all involved, and thanks everyone for listening to official advice. He says people preparing should only buy what they need - three days' worth.
NEMA acting director of civil defence Roger Ball says it is an "unprecedented and dangerous weather event".
"Please stay safe and don't take any chances. We are expecting very high winds and heavy rain today. At 1 this morning, the centre of Cyclone Gabrielle lay approximately 230km nor-nor-east of Cape Reinga."
He says if you find the winds dropping this evening, it does not mean you are through the worst.
"The winds will increase again and come from the opposite direction so you need to be ready to protect yourself and your family throughout tomorrow. Make sure you've prepared your whare for high winds and heavy rain."
He says there are several road closures and advises people who do need to travel to drive to conditions to watch for debris and flooding.
"Please remember, never drive through floodwater."
Northland experienced winds up to 130km/h, Hauraki Gulf 135km/h, and maximum wind speeds at the Harbour Bridge were 110km/h.
Whangārei and Kaikohe received 70mm of rain over 12 hours, with no significant rainfall in Auckland overnight.
Western Coromandel peninsula was buffeted by winds up to 160km/h with speeds up to 110km/h in other areas of the peninsula.
Some 24 civil defence centres and shelters were opened in Auckland overnight, including three mass evacuation centres. He advises people to check with local civil defence for details.
"We understand we have about 58,000 people across the top of the North Island without power. We are working closely with the relevant companies to understand how quickly that can be restored but the indications from those power companies are that it could take some days in some cases."
Meanwhile, there have been some shortages reported, possibly due to panic buying, but McAnulty says Commerce Minister Duncan Webb has been assured by the major supermarkets that supply chains at the moment are "pretty robust".
"We're encouraging people to be mindful of that and only get what they need. In an event like this three days should be enough and if you've done your big shop for the week you might actually already have three days worth of food and water on the property already so please be mindful of that.
"Also just be mindful that as with Covid, people that work at supermarkets are doing an essential service and they will be under strain, so a little bit of patience. The supermarkets will get what you need over time."
He says the slips on SH25A were already significant and has at least doubled in size.
"I've been speaking to the mayor this week and he says it's grown in size again and that's when the rain came so that's a significant disruption for the peninsula. We'll have to wait and see what the weather event brings, there's huge amounts off rain forecast for that.
"Coromandel are incredibly well equipped, I couldn't be more impressed with their local civil defence but they can only deal with what they can as it comes."
He says people have heeded the warnings, from what he's seen, and that makes all the difference.
If people were unable to get their three days supply they should get in contact with their local civil defence if they are unable to stay at home, and provisions may be able to be provided to them.
He says he thinks regular and clear official communications is making a big difference compared to the recent floods in Auckland and other areas in the north.
Defence Force personnel have been deployed to Auckland, Northland, and other areas including Ōpōtiki, "ready to go to help with evacuations".
He says because there was plenty of warning this was going to come, they have been able to provide those resources into those regions to help.
He says the National civil defence operations in the Beehive bunker has been set up and active for 17 days now, and some people have been there every one of those days.
"That gives us a lot of confidence that where possible, support is being provided."
McAnulty says he has not seen any reports yet of health facilities impacted by the power outages.
He warns against risk-taking behaviour.
"Please don't go out in the floodwater, please don't go out in the high swells. We're seeing reports and projections that some of the swells around coastal New Zealand are going to be absolutely massive - look, I'm conscious that some people might find that appealing and they might want to go surfing or whatever - if we think back to the messages in Covid please don't do something that if you get caught will drag emergency responders away from their core task.
"To those where the weather hasn't hit but it's projected to, please use the time that you've got to get prepared. As we've seen in those areas that have now been hit, using that time to get prepared can make all the difference."