The girl was conscious and alert when she was transported for evaluation, MBTA Superintendent Richard Sullivan said in a statement. Officials did not release her age or further details about her condition.

The MBTA is investigating the facts and circumstances of the incident, Sullivan said. The agency did not say how the girl came into contact with the third rail, which carries the high-voltage current that powers trains, or whether she was on the tracks at the time.

The Jackson Square station, on the Orange Line, sits on the border of Jamaica Plain and Roxbury and serves as a busy transfer point for buses and trains in the surrounding neighborhoods.

Third rails are a persistent safety concern across the transit system. The electrified rail runs alongside the tracks at ground level in many outdoor sections of the network, and contact can cause severe burns or fatal electric shock. Transit agencies nationwide have faced questions about fencing, signage and platform barriers meant to keep riders away from the tracks.

The MBTA has not said whether any safety changes will follow the investigation. Officials did not immediately respond to questions about the girl's condition or the circumstances that led to the injury.