There were a number of fires around the country last night - including a massive blaze on Mt Wellington - with fireworks believed to be the culprit.
Enormous plumes of smoke were rising up over the north side of Mt Wellington, enshrouding the city.
There was no road access, so firefighters were forced to roll out "hundreds of metres" of hose. A helicopter could be seen circling above the hill.
The blaze - which just before 10pm - at its peak was 200m by 100m with multiple crews working to extinguish it, Fire and Emergency NZ shift manager Carren Larking said.
Seven appliances and a water tanker were on site.
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"We've had multiple reports of people seeing fireworks in the area," she said.
At 12.10am, Larking said firefighters were dampening hot spots.
She said they had had several calls from members of the public in the central city who could smell smoke inside their homes and offices which she put down to the hill fires.
Olivia Drew was at the scene and told the Herald: "Some guy came over and told us there were a bunch of young adults and they'd been letting off fireworks and then it just caught on fire. Then they ran away obviously and we ran over to see it when it was just starting. And now you can see that it's massive."
Another witness said there was a group of youths on the hill with sparklers.
There was "a really loud bang" and then the fire started.
"It spread quite quickly".
Senior Station Officer Toby Kerr told the Herald at the scene: "It was quite visible from all over Auckland. There were earlier reports of fireworks been let off at the summit, but that's unconfirmed."
He said reports of fireworks were "a concern".
"It's been a busy night and the fine weather leading into Guy Fawkes hasn't helped us.
"We advise people to act responsibly, within safe practices and hopefully do it somewhere around where water is available, not on top of our mountains across Auckland. There isn't a lot of water to help us fight this sort of thing."
He expected a presence at the scene for "quite some time".
Earlier, a firefighter could be heard yelling at bystanders: "This is not a viewing platform. This is a fire. Get off the mountain".
Another was heard saying the blaze was "getting bigger" and that they needed Howick's mobile pump.
Meanwhile, Fire and Emergency services shift manager Murry Dunbar said they were called to a fire on Mt Eden around 10.10pm.
The fire was now contained to the crater and five trucks were working to extinguish the blaze.
"It's pretty safe to assume it was caused by fireworks," he said.
A man who walked up Mt Eden to watch fireworks in the city said the fire was "50m wide and growing" when fire trucks arrived.
Travis Mischewski earlier said the fire was growing closer to the tower.
"A huge cloud has formed from a massive grass fire. Potentially up to 60 meters wide at its widest point."
There are also two scrub fires in Ranui, with two trucks at the scene.
A local reported to a community Facebook page that they had seen a fire near the Ranui and Sturges Road train station.
In Christchurch, a large hedge fire was believed to have started by fireworks tonight, NewstalkZB host Chris Lynch reporter.
Carl Taylor lives five houses from the massive blaze in the subdivision of Waitikiri, Burwood.
He said the flames were "higher than the roof." It's understood no one was hurt.