Updated at 3:07 p.m.

More than 200 passengers were forced to evacuate after a fire broke out on a 42-year-old Orange Line train that was crossing the Mystic River approaching Assembly Station this morning.

MBTA spokesman Joe Pesaturo said passengers noticed smoke and flames from the first car around 6:45 a.m. While most of the riders walked off the train through a rear car, others panicked and kicked out windows to escape the smoky car where the fire occurred. One woman jumped off the bridge into the Mystic River. Rescue units went to her aid, but she declined medical attention. Despite the chaos and confusion, no injuries were reported.

At an afternoon news conference, MBTA General Manager Steve Poftak revealed that a sill — a piece of metal on the side of the car — broke off and made contact with the third rail, “causing an ignition.” Poftak said that produced sparking, some explosions and a smoky fire. By the time fire personnel responded, the fire apparently had died out. Poftak said that may have been due to the fact they turned off electrical power provided through a third rail within 2 minutes of the incident.

Gregory Bouchard was riding in the car where the fire broke out.

“It was very scary, just, you know, not knowing what’s gonna happen,” Bouchard said. “I got on the phone to my husband, and he called 911 and alerted some of the news people.”

Bouchard said that T workers on the train were trying to keep everyone calm and get them farther back in the train. Once they got off, he and other passengers were told to walk back to the Wellington station.

“I will say that most of the passengers were staying as calm as we could, and the T people were doing a great job, and a lot of people were stepping up and trying to keep each other calm,” Bouchard said. “But several hundred people, it was not a fast thing to get people off the train. I think it took about 10 minutes for me to get off.”

Videos and photos from riders showed plumes of smoke and flames, as well as people evacuating the area.

Shuttle buses replaced service between the Oak Grove and Community College stops for about four hours until regular service resumed on the line, and the Haverhill Line Commuter Rail trains made additional stops at Oak Grove to accommodate an overflow of passengers.

The fire marked yet another serious safety incident on the T.

Poftak noted that the train in question was first put into service in 1980 and was last inspected on June 23 of this year, and no issues were reported with the metal piece that came loose and sparked the fire. Poftak said all similar 1200-series cars are inspected every two to three months. In addition, every other Orange Line car in service was inspected for loose sills after this morning’s incident, but no issues were found.

The MBTA is in the process of replacing its entire aging Orange and Red Line fleets at a cost of $2 billion, but that process is taking longer than anticipated due to the COVID-19 pandemic and supply chain issues. Sixty-four new Orange Line cars and six new Red Line cars have been delivered so far out of 152 new Orange Line cars and 252 Red Line cars on order.

Poftak said the National Transportation Safety Board and Federal Transit Administration have been notified about the fire. The FTA is already investigating safety issues at the T, with the agency's final report expected in August.

Bouchard said he was "lucky" that his boss allowed him to take the day off work after the accident.

"It's unfortunate to be a commuter who has to work in Boston right now," he said, acknowledging this was not an isolated incident. "But I have to work in Boston. So I'm not sure what tomorrow's going to bring."