University of Otago campus police officer Senior Constable John Woodhouse, of Dunedin, said a party at the corner of Castle and Howe Sts on Saturday that attracted 400 to 500 people presented no problem to police, but trouble started after "things went quiet''.
"They [non-students] are attracted to Orientation and they are causing [problems],'' Snr Const Woodhouse said.
The 16-year-old youth and a 19-year-old male associate, who was charged with possessing a knife, were from Caversham, and unemployed, he said.
The 16-year-old was referred to Youth Aid and his associate would appear in the Dunedin District Court on Friday.
A 17-year-old high school pupil, who was allegedly breaking bottles in the street, and a 19-year-old St Kilda man and an 18-year-old Outram man were also arrested in North Dunedin on Saturday.
The older two had been charged with disorderly behaviour.
"We'll take what action we can within the law to keep these students safe,'' Snr Const Woodhouse said.
"If you offend in the student area, you will be prosecuted.''
Damage to three flats that were entered during the weekend was possibly committed by non-students too, he said.
The flats were ransacked in what police are describing as "mindless, senseless'' acts.
Senior Sergeant Liz Waru, of Dunedin, said two flats in Castle St had windows smashed, and in one of them a television and printer were thrown against a wall and holes punched in walls.
At a flat in Leith St North, a door was ripped off a dryer and the kitchen was "ransacked'', including the drawers being pulled out of the refrigerator.
Police were treating the incidents as burglaries, although the only thing stolen was a box of beer, she said.
All three incidents happened between 4pm on Saturday and 5am on Sunday.
Police had forensic evidence from two of the three addresses, but were looking for help from neighbours to curb these kinds of incidents, Snr Sgt Waru said.
"That's just mindless. It's senseless. We would hope that if there are people nearby that hear the noises, that they would call us.''
Patrols had been stepped up in the student area during Orientation Week, she said.
