Gladesville Superintendent John Duncan told reporters the matter is being treated as a homicide.
"This is a very, very serious matter and we hope to get to the bottom of it," he said.
Police were called to the home just after midnight local time following a fight among young partygoers that left six males, including Aidan, and a female with stab wounds.
While Duncan could not confirm what weapon or weapons were used, he said the fight broke out among the about 50 partygoers, not gatecrashers.
"We do not believe there was an involvement of gatecrashers. For some reason it's turned violent and that's what we need to get to the bottom of," he said.
The 16-year-old was rushed to Westmead Hospital with critical injuries shortly after the incident.
The five other injured partygoers are being treated at hospital.
Police hope to speak to them soon.
Police are speaking to witnesses and no arrests had been made yesterday.
- AAP
