A third male was arrested after police were called to a fight near the carnival ride section about 8pm tonight.
Police said they found two males suffering stab wounds and gave first aid before paramedics arrived.
They said both suspected victims were taken to Westmead Hospital, and one was in a critical condition, before later confirming one of the youths had died.
Showgoers were moved out of the area and a crime scene was established.
Videos of the moments leading up to and following the incident have been shared extensively on social media.