Fire crews have put out a huge blaze on Auckland's Mt Wellington, which is thought to have been started by fireworks last night.
Elsewhere, firefighters were called to more than 50 fireworks-related blazes throughout the country overnight.
The Mt Wellington blaze was significant, with multiple crews working to extinguish the mammoth 200m by 100m inferno on the north side of the mountain.
Enormous plumes of smoke could be seen across the clear sky late last night and smoke could be smelt across the city before the fire was fully extinguished about 2am.
There was no road access, so firefighters were forced to roll out "hundreds of metres" of hose, while a helicopter could be seen circling above the hill.
• Blazes on Mt Eden and Mt Wellington in Auckland
• Fireworks shot from cars and aimed at buildings, vegetation
• Bay fire crews on high alert as sky sets to light up for Guy Fawkes
• Two large blazes burning in Hawke's Bay and Nelson
It comes as anti-fireworks groups head to Parliament next week to lobby for a ban on private sales.
A select committee is hearing submissions on the issue after three separate petitions to ban fireworks sales garnered thousands of signatures.
But fireworks importers will also be speaking to the select committee, and they think the silent majority of the public is on their side.
The Government says it currently has no plans to change the law around fireworks.
Meanwhile, fire crews in the upper North Island were called to 55 fireworks-related blazes in the past 24 hours, Fire and Emergency said early this morning.
Fire and Emergency shift manager Carren Larking said they had received several calls from members of the public in the central city who said they could smell smoke inside their homes and offices, which she put down to the hill fires.
At the scene last night, City senior station officer Toby Kerr said: "It was quite visible from all over Auckland."
Kerr said there had been earlier reports of fireworks being let off at the summit. However, those had not been officially confirmed.
It had been a busy night, he said, and fine weather this week had not helped.
"We advise people to act responsibly, within safe practices and hopefully do it somewhere around where water is available - not on top of mountains across Auckland.
"There isn't a lot of water to help us fight this sort of thing."
Another blaze in the crater of Mt Eden was also put out by about 2am, authorities said.
Fire and Emergency services shift manager Murray Dunbar said they were called to a fire on Mt Eden around 10.10pm.
"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 "50 metres wide and growing" when fire trucks arrived.
Further south, there were eight call-outs in Christchurch, including a fire that destroyed a hedge on Blue Stone Drive in Parklands.
The 55m stretch of hedge separates houses from a golf course.
Local man Carl Taylor, who lives five houses from the massive blaze in the subdivision of Waitikiri, Burwood, and said the flames were "higher than the roof".
Nine call-outs in the lower North Island were attributed to fireworks, while authorities in the upper South Island, Otago and Southland reported a uneventful night.