It happened as the man was exiting the northbound 4 train at 176th Street and Jerome Ave. in Morris Heights just before 9 p.m. on Thursday.
He was stabbed in both the back and chest with an unknown object.
Police say the attack was unprovoked.
The suspect is described as a man with a dark complexion, about 5'11, and was last seen wearing a dark-hooded sweatshirt and Nike sneakers.
The victim was taken to St. Barnabas Hospital where he is in critical condition.
ALSO READ | Who is the NYC rooftop jumper? Eyewitness News solves mystery behind viral daredevil stunt
Man explains mystery behind viral video of NYC rooftop jumper
----------
* More Bronx news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube
Submit a tip or story idea to Eyewitness News
Have a breaking news tip or an idea for a story we should cover? Send it to Eyewitness News using the form below. If attaching a video or photo, terms of use apply.