Two attacks in central Auckland by children as young as 10 are being described as vicious and alarming.
Seven children have been referred to Youth Aid, while two girls aged 16 and 17 have been arrested.
Police said up to six people brutally attacked a couple, and tried to confront another man, in Myers Park on Saturday night.
In a separate incident the night before, police said five people, some as young as 12, assaulted a bottle-store worker and stole alcohol in Karangahape Road.
The group then went on to hide in the nearby park.
Inspector Gary Davey said while it was not unusual to pick up children of that age in the city, the nature of the attacks was alarming.
"What's disturbing about it is they actually lay and wait for their victims to walk down through Myers Park and then basically all jumped out and attacked one man - he was able to defend himself and just received a bloody nose.
"They then waited for another couple to walk down and then viciously attacked them, hitting them about the head and body, kicking them, also throwing the young woman to the ground several times while trying to rob them."
Both groups of young people were detected by newly-upgraded cameras and lighting in the area.
Mr Davey said police were still looking for one person in relation to the Myers Park attack.
However, Barbara Holloway, the head of a local Auckland business association said random violent incidents happened all over the city, and the crime rate was dropping.
Ms Holloway, head of the Karangahape Road Business Association, said that the area had a very low crime rate, and it was continuing to fall.
She added that their security guard in Myers Park reported mostly seeing families there.