The incident happened on a second-floor fire escape on Georgia Avenue in East New York around 4 p.m.
Authorities say the person who was shot, a 27-year-old man, was wounded in the groin and the leg.
He was rushed to Brookdale Hospital, where he is listed in critical condition.
There was a massive police presence in the area as they searched for the suspect.
So far, no arrests have been made.