The teen was one of three people stabbed in two separate incidents overnight.
Two men were arrested after a stabbing in Cockatoo, south-east of Melbourne, which left a man in his 50s with severe injuries.
Another man was taken by road ambulance to hospital after the incident, which occurred just after 11.30pm on Saturday at Boronia Crescent.
Detectives believe four men were involved in the assault, but a motive for the stabbing is still unknown, the spokeswoman said.
“The exact circumstances surrounding the incident are still being established,” she said.
The victim in his 50s is believed to be in a non-life threatening condition.
Two men, aged 21 and 26, were arrested nearby and are currently assisting Casey crime investigation unit detectives. Police are not looking for anyone else.
Anyone who witnessed the incident or who has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au