Police believe visitors are largely behind the dangerous disorder offences that plague Dunedin during student Orientation Week.

Five people were arrested overnight as drunk young people spilled on to the city's streets.

Inspector Kelvin Lloyd told ONE News that visitors to Dunedin are behind many of the disorder offences related to Orientation Week.

"There's a perception that when there's disorder associated with Orientation Week, it comes back on the bad behaviour of students," he said.

"What we're finding is people coming from outside Dunedin to join in on events."

Mr Lloyd said the pattern of outsiders to the area getting picked up for offences is a concern for police.

"The vast majority of the student populations are absolutely brilliant to deal with. It's the minority causing issues.

"In a lot of cases it's not residents or students."

Senior Sergeant Darryl Lennane said the arrests last night were related to out of control drunken behaviour at parties.

Four of those arrested were given pre-charge warnings related to disorder meaning they won't go to court. One of those arrested was a student.

Emergency services were also kept busy with firefighters called out to three couch fires set alight outside student flats.

Students loudly booed fire officers as they attempted to douse the fire.