Thick gray smoke billowed out of the 191 St No.1 train station on Tuesday afternoon.
FDNY Deputy Assistant Chief Mike Woods said the train hit "some kind of piece of equipment" as it entered 191st Street subway station, which then made contact with the third rail and created a smoke condition.
18 people reportedly had minor injuries and were evaluated on scene.
2 people refused medical attention and 16 people were taken to area hospital, officials said.
Emergency responders assessed nine patients, all suffering from smoke inhalation, FDNY officials said.
Woods confirmed there were minor smoke inhalation-type injuries but were assessed by EMS.
Despite the heavy smoke, Woods said there was "no active fire in the train."
The fire was put out and subway service was temporarily suspended in both directions between 145th Street and 215th Street.
Trains are back to normal in both directions after a rail was replaced at 191 St.
Authorities do not believe anyone was responsible for leaving the object on the tracks, but transit officials will continue their investigation.
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