It happened around 8:20 p.m. on Wednesday.
The bay is situated in the middle of the emergency room, partially indoors. The water leak was almost totally contained to the ambulance bay, except for a small amount of water that leaked into one side of the emergency room.
A spokeswoman said patient care was not affected. No one was moved or evacuated. The water never came close to patients.
The hospital is on ambulance divert until the pipe is repaired and the water is cleaned up. Ambulances will go to other local hospitals, including Lutheran, Coney Island, and Methodist.
The emergency room is fully operational and the walk in entrance on 49th Street remains open to the public.