The incident happened around 3 p.m. at 2819 Mermaid Avenue in Coney Island.
Police say a 17-year-old boy was chased by a group of kids who eventually caught up with the victim and began to attack him.
One of the suspects then took out a knife while the others continued to attack and stabbed the victim in the back.
RELATED: Eyewitness News is tracking crime and safety across New York City and in your neighborhood
Authorities say the victim walked into a nearby business for help. That business then called 911.
The victim was taken to Maimonides in critical condition.
No arrested have been made and the investigation is ongoing.
----------
* More Brooklyn news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube