Central Whangarei is the most common place for assaults or robberies in Northland, according to figures released by Statistics New Zealand.
There were 87 victims of assault, sexual assault or robbery in public places in central Whangarei last year.
Whangarei firm Northern Districts Security managing director Jean-Pierre Dignon said staff often saw fights, and said alcohol and drugs were "massive" contributors to aggressive behaviour. Patrols operated in the central city from 12am to 3am on weekends. He said the most common time for violence was 3am, after bars closed and staff would see between two and five fights a weekend.
"Some are really small, but some would involve a group of people or two groups of people fighting, and there would be 20 people involved. That might be one incident," Mr Dignon said.
He said police responded quickly when contacted about a violence, but police resources were limited.