The fire broke out on an escalator in Concourse C and spewed smoke through Terminal 8 around 7:15 a.m.
About 960 people were evacuated from the area and taken to another part of the terminal. Nine people were injured -- all with minor smoke inhalation -- and four were taken to the hospital to be checked out.
The FDNY has checked the entire terminal which is now being ventilated.
The terminal is occupied by American Airlines and so far 69 flights have been canceled and 376 of their flights have been delayed -- which is 10% of the airline's flights.
The airport suggests checking with your carrier before traveling.
The exact cause of the fire is under investigation.