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Bottles were thrown at police during clashes with students in Dunedin last night, leaving so much broken glass ambulance crews were forced to abandon their vehicles and go into troubled areas on foot.
One crew member called back to the ambulance base saying "we may need to wear our hard hats if we go out again".
Police reported 30 arrests late last night after the arrival of the annual Undie500 convoy of Canterbury University students to Dunedin.
It was a reprise of the violence of last year, which saw about 100 students in court after a weekend of bottle-throwing and couch-burning.
Last night, more than 50 police officers in riot gear struggled for hours to break up large groups of disorderly students.
They began throwing bottles, attacking police officers and vehicles.
An ambulance communications spokeswoman for the area said the scene was chaotic.
"It's just chaos down there... Every time our crews go out it's just absolute bedlam," she said.
The trouble was concentrated in Castle St, Howl St and Dundas St.
They are areas near Otago University often referred to as "student ghettos".
"The students... down there, they're throwing bottles and lighting fires and they smashed a back window of a police car...
"They're moving towards town, this big group...
"Police are in their riot gear and trying to keep them contained.
"This big group of them are just swarming towards the rescue services."
At midnight, only minor injuries had been reported. One girl had been hit by a bottle, another person had suffered a cut hand.
The trouble followed a day of sporadic fires and roaming parties which intensified as the evening wore on. By 9pm, the fire service was stretched having to contain more than 50 small fires connected to student problems.
Police were calling for reinforcements from outlying stations to reinforce officers struggling to contain trouble, which was likely to continue today. The reinforcements included officers being driven up from Invercargill.
