Puddles of blood formed on the driveway of the Rotorua home where the stabbing took place about 10pm on Friday.
A 15-year-old has been arrested and charged with assault.
He appeared in Rotorua Youth Court, charged with assault, and was remanded in custody to reappear on Thursday.
A post-mortem examination was completed yesterday, but police would not be making the results public at this stage, said Detective Senior Sergeant Mark Loper.
Mr Loper said today detectives and forensic experts were continuing their examination of the scene, and speaking to numerous witnesses.
Yesterday Rotorua community leaders called for the Government to tackle youth and alcohol problems in the city.
Last month 11 teens were lucky to survive a van smash. In March, police intercepted a group of youths armed with a knife, wheelbrace and an iron bar on their way to attack students from another school
Tamm said there appeared to be a small party going on at the Clinkard Ave house where the stabbing took place.
"I heard all this screaming and yelling, and we could hear someone banging on the door [of the house] saying 'Let me in, let me in'. Then I could hear a girl saying 'he's not breathing'," said Tamm.
"I waited for a bit but then decided to go over and see what was happening.
"A young Maori girl was standing outside and she looked at me and said, 'Look, I've got blood all over my hands'. I went over there and there was blood everywhere.
"The boy was face down on the ground but was sort of breathing or choking ... there was so much blood."
Tamm said one of the girls passed a phone to him so he could talk to a 111 operator.
"They kept telling me to find the wound but I couldn't see anything. ... I rolled him over and when I did his eyes went into the back of his head. I started doing CPR and he kicked up a couple of breaths, and then he just shut down.
"I couldn't see a wound on him, I didn't even know he'd been stabbed, he was just saturated in blood."
Tamm said the teenagers had been drinking.
"'I could smell it from a mile away. I can still see his face when his eyes rolled back ... it was just awful. He's someone's kid. I don't know what happened ... but I prayed for that boy. "
Rotorua district councillor Charles Sturt said the killing was "indicative" of youth issues in the city.
"We've got people that talk up that we haven't got any issues in Rotorua. But there are specific issues that need addressing and we need some strategies in place to fix those problems," he said.
Deputy Mayor Trevor Maxwell was shocked when told about the death.
"I'm horrified. It's awful. We're still trying to work through all the issues from things like Nia Glassie."
And councillor Geoff Kenny said it was a "terrible tragedy".
"It's another example of young people not knowing the consequences of their actions."