Wellington  - New Zealand police arrested about 20 students after a riot in the university city of Dunedin, according to news reports on Saturday.

More than 600 students pelted police with bottles and bricks, set fires to furniture and rubbish in city streets and tipped over a car during Friday night's riot, Radio New Zealand reported.

Police inspector Dave Campbell said one officer collapsed after being hit on the head by a bottle. Police wearing riot gear took two hours to disperse the crowd with pepper spray.

The riots followed the arrival in Dunedin of carloads of students from Canterbury University, in Christchurch 360 kilometres to the north, on an annual pub crawl that has caused mass disturbances in the past.

The event, dubbed the Undie 500 because only cars worth less than 500 New Zealand dollars (350 US dollars) participate, was cancelled last year after it resulted in 69 arrests the previous year.

The arrested students, most from the city's University of Otago, were charged with disorderly behaviour, breaching a liquor ban and starting fires. (dpa)