Police are grappling with at least their sixth public violent gang confrontation in as many weeks as gang numbers in New Zealand continue to rise.

However, police won't say just by how much but a leading researcher into the history of gangs has labelled it a "resurgence".

And Dr Jarrod Gilbert warns that with an increase in numbers it will mean an increase in crime.

The latest gang shooting saw Mongrel Mob member Kevin Ratana shot dead in the street last Tuesday. So concerned about the sudden influx of gang members and possible retaliation, police increased their numbers and sent its Eagle helicopter to the area to monitor mourners.

The first most notable sign of ructions this year happened in Hamilton when 23-year-old Robert Nelson was shot dead defending his girlfriend in her Matthews Ave home during the early hours of the morning.

Nelson ran to the aid of his partner, 21-year-old Kahlee Marfell, who had just been shot in the leg after three intruders, at least one of whom was armed, stormed into the Matthews Cres, Melville, home during the early hours of July 8.

The Herald later learned Nelson, who isn't linked to any gangs, was in the wrong place at the wrong time and the gunmen were there to find Marfell's father, Mark "Griff" Griffiths, a senior Mongrel Mob member.

Seven weeks on, police are still hunting those responsible and no arrests have been made.

A few days later, Ngaruawahia man Mitchell Paterson, 27, was found in a body of water under a bridge at McLaren Falls.

Multiple people have been arrested in connection with his death, some of whom who have gang links.

However, the most recent fiery confrontation was the drive-by shooting of Ratana.

Ratana, a 27-year-old father of two, was shot dead on Puriri St and was farewelled in the town today.

A parent who is associated with a gang was also identified at a brawl at Rosehill College on Friday.

About 150 people were involved the fight and claims it involved both students and parents.

Two students from the school reported that the parents were from rival gangs, believed to be the Mongrel Mob and Black Power.

And in Hastings on Saturday night, another clash believed to have involved Black Power and Mongrel Mob members happened at a 21st birthday at Moteo Marae.

Shots were fired and a woman was stabbed while two men were also hospitalised with injuries.

Gang Intelligence Centre figures released in June showed gang violence, nationally, had dropped by 10 per cent.

The only police district it had spiked in was central, which encompasses Taranaki, Whanganui and Manawatu, which was up 41 per cent.

Cathy Toi-Cassidy, manager of the Intelligence Centre confirmed they'd seen a rise in numbers.

"We have seen gang membership numbers increase in recent years, however some of that can be attributed to better information and intelligence.

"Adult gang members represent 0.1 per cent of the population but are over-represented in violent criminal offending."

Gang researcher and sociologist Dr Jarrod Gilbert said there had been a "remarkable" resurgence in the number of gangsters in New Zealand, which in turn had led to an increase in crime.

"There does appear to be an increase in numbers throughout New Zealand and when there's an increase in numbers it's likely it will lead to an increase in problems.

"There has been a resurgence in the youth for a long time. It looked like the gangs in large part were ageing themselves out but what we've seen is a rejuvenation in recent times.

"They've come back into vogue, it's a remarkable turnaround for a scene that was in pretty ill health for much of the early 2000s."

He said the concerning issue with gang violence was the often "tit for tat" or retribution situation.

"And if you don't get on top of that it can spiral out of hand very quickly."

As for his thoughts on the police call to launch their Eagle helicopter during Ratana's funeral, Dr Gilbert labelled it a "symbolic gesture" to show how seriously they're taking the shooting and to try deter any future violence.

Acting Detective Inspector Mike Varnam, Programme Manager – New Zealand Gang Strategy, said they were "extremely concerned about this serious offending occurring in our communities".

"We take any occurrence such as these incidents very seriously and are working to ensure people are held to account for these crimes.

"We have dedicated investigation teams working across each of these matters and national support is provided wherever necessary.

"A number of charges have already been laid in relation to the death of Mitchell Paterson and strong lines of inquiry are being followed in relation to the recent homicide in Whanganui and the incident at Mateo Marae this weekend. Police have also taken a number of steps to appropriately manage the recent incidents at Rosehill College."

Varnam said police were aware that gang violence could be unsettling but they were doing "everything we can to resolve these crimes and prevent further incidents from occurring".

He hoped the increased police presence in Whanganui brought some reassurance to residents, he said.