A teen is fighting for his life after police sources say he fell while subway surfing on Monday afternoon.

Police sources say it happened at the Baychester Station near East 180th Street and Eastchester-Dyer Avenue. This all happened Monday at 3 p.m. on a northbound 5 train.

Witnesses on the train say they've seen the teen along with others subway surf regularly. Police sources also confirmed there was another person subway surfing at the same time. The teen, who is in critical condition, is between the ages of 14-16.

The NYPD is warning that it is illegal to subway surf and says six people died doing it last year.