Teenagers mounted the roof of a Whangamatā cafe on New Year's Eve, throwing bottles at police who armed themselves with shields and batons.
Auckland woman Jane Phare is on holiday in the Coromandel town with seven teenagers, including her 15-year-old son, and had ventured out to check on the teens.
She said there were thousands of teens gathered on the streets. Some had climbed onto the roof of Blackies Cafe, next to the Whangamatā Surf Club, which is about 200m from her friend's bach she was staying at.
"There was just this roar of out-of-control drunk kids and no music," Phare said.
"There was a huge crowd of drunk teens who had climbed up on the roof. They were throwing bottles at police - there were bottles flying everywhere, smashing onto the ground.
"The road littered with broken glass and police trying to keep young ones arriving away from bottles crashing down. Police were telling us to stay back.
"Riot police with shields and batons arrived at the club and everybody scattered. They've arrested quite a few teenagers. There's a paddy wagon and you can hear thumping inside."
She said the riot appeared to be started by bored teenagers.
"There's nothing for kids to do. They're too young to go to a festival. They drink at home because there is a liquor ban and they're drunk and a bit bored.
"There were cars and people on every verge."
Police and Fire and Emergency have been contacted for comment.