'Dunedin is cleaning up after alcohol-fueled students rioted in the city last night, pelting police with bottles and setting cars, mattresses and couches on fire.

The rioting, [...] centred in the heart of the student area of North Dunedin, was triggered by excess alcohol in the wake of the student Undie 500. [Not to be confused with this.]

...Mr Ross said police were at one of the flats talking to the occupants when they began to be pelted with bottles.

"It was totally unprovoked."

It took police, with extra reinforcements from outlying areas, until about 11pm to bring the crowd under control.

Police and fire crews were lucky to escape without any serious injury as students threw bottles and set cars alight, he said.

"Some police have got some nasty grazes from flying bottles."

...While he did not know what triggered the students to riot, Mr Chin said the length of time people had been drinking had to be a major contributor.

Partying outdoors, from the early hours of Saturday morning when the students started arriving, had been helped by an unusually warm weekend for the city, he said.

Mr Chin said the rioting came at a time when the culture of the university had been broken down and Otago university past-times such as couch burning had been phased out.

"Things had been working extremely well."

The majority of students at Otago were there for the education and a minority was spoiling it for them with their bad behaviour, he said.

"I'm really pissed off with what's happened."'