They arrived in five cars in the early hours of Sunday armed with softball bats, iron bars, axes and hammers.
After smashing up two cars in Norrie Smith Ave, Flat Bush, the street gang known as the Junior Crip Boys turned on a local "street crew".
The street crew were outnumbered, and two young men were severely injured in the attack.
And - though police still are not sure how it fits in with what happened - a man known to both gangs was later found dead in his nearby home with a knife in the chest.
Police say street youth gangs are an escalating problem that staff cannot combat on their own.
Detective Senior Sergeant Sue Schwalger said police were the "ambulance at the bottom of the cliff" and the gang problem should be tackled by the wider community.
"The police are only one small agency, and we can only do so much."
Police will not name the gangs involved, but residents spoke openly of the GBF and JCBs.
The victims belonged to the Gambino Family [GBF] street gang, local members said.
Three of the youths who spoke to the Herald all gave their surname as "Gambino" and described GBF as a "street crew" with 30 to 50 members.
Last night, an 18-year-old was in a critical condition in Auckland City Hospital. A second victim was in a serious but stable condition in Middlemore Hospital.
Police have a piece of wood believed to have been used in the attack but no other weapons have been recovered.
Around midday on Sunday, as they investigated the alcohol-fuelled bashings, they were told about the body of the man who lived nearby.
The Herald has been told the man's son is a member of the JCB gang.
Neighbour Risati Tiatia found the Samoan man, a father of four who lived alone, with a knife in his chest in the house about 200m from where the fight took place in the area of Norrie Smith Ave and Dosina Place.
Mr Tiatia and his wife, Miriama, knew the man well and Mr Tiatia dropped him at work in Papatoetoe every day.
They last saw him on Saturday night.
"He was a loud mouth," Mrs Tiatia said. "If someone didn't know him they would just punch him or try to pick a fight."
Ms Schwalger said police were dealing with an increasing number of violent assaults involving a growing number of youth gangs.
"The criminal youths of today don't stop once a person hits the ground. That's not their culture, and it is escalating.
"We are getting a large number of these types of incidents. We are lucky we only get the seriousness of this scale once in a while; however it is escalating."
The gangs are geographical and identify themselves with the colours of the ethnic gangs such as Mongrel Mob and Black Power, but often they are not affiliated to those established outfits.
Ms Schwalger said more youths were getting involved because gang members recruited their siblings and set up factions within schools after they left the education system.
"We need to have a collective group that will target this and we need to start from the bottom up," she said.
"We need to start from kindergarten through to the schools and high schools ... otherwise it will get worse."
The district's gang problem was recently highlighted on the Police Ten 7 television show.
Police were called to a gathering of school students in Otahuhu and confiscated knives and hammers from the teenagers.
Constable John Chapple told the show the youth gangs were taking up more and more police time and gang members "think they're living in South Central LA".
He said it was "just a matter of time before someone is killed".
Teen gang turf wars a deadly problem
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