Emergency services were called to an address on Carnegie Street in Chifley about 8.25pm following reports of a brawl.
Police were told around ten people, two of whom were armed with machetes, approached a 16-year-old and an 18-year-old at the front of the house.
One witness told 9News the uninvited guests were dressed in ski masks.
They allegedly fled the scene before officers arrived.
Police believe the incident was a targeted attack.
Paramedics treated the 16-year-old at the scene for laceration to his back and legs and he was taken to Royal Prince Alfred Hospital in a stable condition.
A crime scene has been established and police have commenced an investigation into the incident.
Anyone with information is urged to contact police or Crime Stoppers on 1800 333 000.
