More serious charges may be brought against the ringleaders of the riot at BW Festival in Gisborne that ended in 63 arrests.
As police issued an appeal for more video footage of the violence, officers said they had found evidence on social media that suggested the violence had been planned in advance.
Tairawhiti area commander Inspector Sam Aberahama told Radio New Zealand this morning that those arrested faced an array of charges ranging from disorderly behaviour to assault with a weapon. However, police were considering charging some those arrested with inciting a riot.
Inspector Aberahama said certain comments on social media indicated that "there was going to be a breach of the fence between two camps".
He said in the "hearts and minds" of the troublemakers, "they had a plan and they were going to carry it out". The Herald could not immediately reach him to query whether messages on social media could or would be used as evidence in prosecution.
Senior Sergeant Steve Sutherland said police were keen to view any video footage of the riot taken by people who were in the area at the time.
"Our investigations into the incident are continuing and it doesn't stop when people have been arrested," he said. "We want to see as much footage as possible so we can identify those who took an active part in the riot."
Police have also been viewing numerous videos posted on media and social media sites.
It was likely many more people had recorded parts of the riot on their cellphones.
"It would be very helpful for our investigation to gather as much information as we can and we hope those who hold that information will be able to assist us."
The appeal came as organisers of the party admitted the event's future was in jeopardy.
The large-scale disorder, sparked by a small group of males torching tents, soon attracted a "mob mentality" and spread across two BW Summer Festival campgrounds.
Police battled with the drunken mobs for three hours.
The trouble started about 5.30pm when groups of festival-goers in the BW campground in Watson Park on the city beach front confronted each other across the fence that divided their two zones.
In the end, 83 people were injured, including seven who needed hospital treatment.
Officers, security staff, camp workers and fellow revellers were pelted with full cans, tent poles and other objects while vehicles were overturned, fights broke out, and dozens of tents and air mattresses were torched.
"It was pure luck that someone didn't lose their life," Inspector Aberahama said. Videos and eyewitness accounts emerged yesterday showing the extent of the destruction.
Amelia Hooper, 19, and three friends - all of Devonport, Auckland - arrived at the BW campground on December 29. The first two nights had passed peacefully before the "complete chaos" of New Year's Eve. "Mostly young boys" with lighters torched tent after tent, she said.
Many others were flattened by people jumping over them. Groups then began charging fences between camp sites, sparking fights, and throwing assorted missiles.
"I had my boyfriend bat away a can that could've split my head wide open. They were just flying everywhere," said Ms Hooper. "We had to get out of there."
Another witness who didn't want to be named said people starting throwing objects and then began to tear down the fence. "Security arrived and everyone got jammed up in one area and that's when the whole thing really blew up," the witness said.
Three 18-year-old boys from Hamilton at their first Rhythm and Vines festival saw it all happen. "It was bloody wild, I wasn't expecting that," one said. "There was no real fighting, mostly the two groups were throwing things at each other, full bottles and cans of alcohol, tent gear, lots of things," said one of his friends.
A woman in her mid-20s from Taupo said one of her girlfriends suffered a gash across her chest and another friend had a broken nose, both caused by flying bottles.
"The whole festival was really good apart from that stupid confrontation and it got a bit frightening. They were just dickheads who started it."
Inspector Aberahama said the riot resembled a movie scene. "As the two groups battled each other it was like something out of the Braveheart movie and excessive alcohol consumption was the driver of it all.
"Most of the injuries people suffered were caused by missiles that were thrown," he said. "We've had disorder issues at BW in the past but this was the worst it's been by far."
Local authorities said the riot had hurt Gisborne's reputation, and expressed doubt over whether the organisers would at least be again allowed to run a BYO arrangement.
BW Festival organisers were granted a special licence, but they reverted to a BYO status after pressure from festival-goers who had already purchased tickets.
Gisborne District Council lease the land to BW campground and today was "very concerned" about the disturbances.
"It must have been very scary for those young people caught up in the event," Council chief executive Judy Campbell said.
BW campground director Toby Burrows said measures put in place to control behaviour over the five-day event did not work on New Year's Eve.
Campground director Toby Burrows said measures in place to control behaviour over the five-day event did not work on New Year's Eve.
"There were a number of things we did all week to help control the behaviour and they worked very well for the week but on the last day it didn't seem to work. It's pretty early to work out where it went wrong."
There was "definitely a risk" the event would be axed.
"The aim is to continue it but we have to sit down and talk with the emergency services and different parties and come up with the right solutions to make it [safe]."
Elsewhere in the country police reported a fairly quiet night. Bay of Plenty police said most people at holiday hotspots, including Mt Maunganui, were well-behaved. Inspector Scott Fraser credited well-organised events, liquor bans and positive interaction between revellers, police staff and volunteers.
In Auckland scores of revellers poured into city bars for the Britomart Beach Party and thousands jammed the city centre to watch dazzling fireworks from the Sky Tower.
Inspector Kelvin Lloyd said crowds in Queenstown and Wanaka were well behaved with only a few minor incidents.
What is BW Summer Festival?
The R18 event was established in 2004. Originally set up as a single campground to help host thousands of visitors arriving for the Rhythm and Vines festival, it now has several camps within walking distance of each other and hosts more than 16,000 people each season.
What are the music facilities?
Since 2007 the festival has had a neighbouring amphitheatre for live music, with room for up to 14,000 people. It also has a Beach Box stage for live acts and DJs.
What was the festival's lineup?
This year's lineup included Flume, Shapeshifter, David Dallas, Peking Duk, Dick Johnson, Tim Phin, Home Brew, Sticky Fingers and others.
What liquor licence does the festival have?
It allows "limited BYO" but prohibits spirits and RTDs over 7 per cent. The SoundShell is a licensed venue where BYO alcohol is not permitted.
How much are tickets?
A BM-only camping pass starts at $115 while a BM+ Rhythm and Vines combo camping pass starts at $295.
Source: BM Summer Festival website
- additional reporting Gisborne Herald