The shooting was reported on the corner of Fulton Street and Tompkins Avenue just before 2:30 p.m.
MTA officials say a B25 bus was standing in traffic when shots were fired from outside the bus.
After hearing the gunshots, police say the bus driver rode up several blocks up when he was alerted by passengers that somebody was struck by a bullet on the rear of the bus.
The victim, later identified as Lydia Flores, suffered a wound to the left cheek where a bullet grazed her face.
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She was taken to Kings County Hospital and is said to be stable.
Police say the suspect fired several rounds and was wearing a red or orange jacket with a grey bottom, jeans and white sneakers. He is said to be a teenager.
There were 35 customers on the bus at the time of the shooting. No other people were injured.
Authorities say Flores may not have been the only victim in the shooting. Another person walked into the hospital on Tuesday with a gunshot wound and police are working to determine if it's connected.
No arrests have been made.
Craig Cipriano, President of MTA Bus Company and Senior Vice President of Buses, released the following statement:
"Nobody should have to go through this on a bus or anywhere else. Thanks to the heroic actions of the bus operator by driving passengers out of the line of fire, and radioing to get help, a serious incident did not turn tragic. Our thoughts are with the victim to whom we wish a speedy recovery and we are fully cooperating with the NYPD investigation."
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