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.
"Police do patrol, but they're not there constantly. I don't think they've got the resources to supply manpower just to be out there," he said. "It's a higher level issue than a police officer level because they don't have the budget. They also just follow instructions from higher up."
Mr Dignon said the company does not supply bouncers for bars because he doesn't want staff exposed to the fighting and intimidation culture in Whangarei. He said he believed violence has reduced in the last 10 years, but would always continue as long as people drank to excess.
He said he expected the real numbers of assaults to be even higher due to unreported incidents.
In a statement, Whangarei Police Area Commander Inspector Justin Rogers said police "will look to send units" to high-offence areas.
"Police are continually looking to prevent public place violence and deploy officers into the area to do both mobile and foot patrols. A high-visibility presence works to prevent crimes from being committed ... Where we identify a pattern e.g. assaults or disorder occurring at a particular time and location, we will look to send units into those areas to prevent crime from occurring."
He said police worked closely with Whangarei District Council, which has upgraded CCTV around the city and organised foot patrols in the city at night.
Mr Rogers said an "increased trust and confidence" in police may have also led to higher numbers of reported assault.
By number of assaults, 2015
* Central Whangarei - 87 - Population: 174 - 50 per cent
* Kaikohe - 68 - Population: 3915 - 1.7 per cent
* Kaitaia West - 49 - Population: 3093 - 1.58 per cent
* Kaitaia East - 39 - Population: 1794 - 2.17 per cent
* Kerikeri - 38 - Population: 6504 - 0.58 per cent
* Dargaville - 35 - Population: 4251 - 0.8 per cent