A woman jumped from a Boston subway train into the river below after a rail car caught fire on a bridge Thursday, and other passengers leaped out windows onto the tracks, according to authorities.

The woman, who was not identified, jumped more than 30 feet from the railroad bridge into the Mystic River below, said Somerville Fire Chief Charles Breen.

The Somerville Fire Marine Unit, which had been training in the river, gave the woman a life jacket after she refused to board their boat and those of other emergency responders, Breen said in an email. The woman swam to shore as emergency responders kept tabs on her, Breen said.

“Once ashore,” Breen wrote, “she refused repeated offers of medical assistance and walked away.”

Most of the fire went out on its own after the electrical system was shut down, he said.

No injuries were reported, said Joe Pesaturo, spokesman for the Massachusetts Bay Transportation Authority. About 200 people were aboard at the time, the MBTA said.

The incident was the latest to raise safety issues for the Boston subway system. A man died in April after being dragged along a station platform when his arm got caught in a train door, and nine people were injured in September after a station escalator malfunctioned.

In June, the Federal Transit Administration issued a series of “special directives” after an investigation of what it called “long-standing issues with the MBTA’s overall safety program and safety culture.” Problems included delayed critical maintenance, lapses in workers’ safety certifications and an understaffed operations center, the FTA said.

The MBTA said the Orange Line train operator reported flames and smoke coming from the lead car around 6:45 a.m. as it crossed the bridge spanning the river between the line’s Wellington and Assembly stations.

A video posted on the Boston Globe’s website shows smoke billowing from beneath the front of the train and then several women jumping out a window as another passenger helps them from below. One woman who said she was in the rail car told the Globe that she saw flames coming up both sides of the train and that a man kicked out a window after he couldn’t open an emergency exit.

In a tweet, the MBTA said a “preliminary inspection” indicated that part of the train’s metal side panel touched the third rail, which caused the fire.

“We are deeply disappointed that this incident occurred and sincerely apologize to our riders who were on the train, as well as to our ridership as a whole,” the agency tweeted. “With a more extensive inspection already underway, we will take every necessary step to prevent this from happening again.”