A Cambridge Fire Department truck on hand at 9:26 a.m. for an MBTA problem in Central Square on Friday. (Photo: Central Square Florist via Twitter)

Another in a string of troubles with the MBTA rode into Central Square early Friday: an electrical fire on an inbound red line train during rush hour that filled the station with smoke, according to the fire department and T staff who spoke with state Rep. Mike Connolly.

The fire department responded to calls of smoke or the odor of smoke at 9:09 a.m., according to scanner reports and posts on social media.

“It’s smoky as hell down there,” a T staffer was telling Connolly within the hour.

The first signs of trouble came from riders present on the platform as the troubled car rolled in.

“You should have seen people running out of the T,” said Jackie Levine, of Central Square Florist. “There was so much smoke.”

The problem was of “unknown origin” but had disabled an inbound train, MBTA dispatchers told Cambridge firefighters, according to scanner reports. Firefighters said T workers “believe the train is dragging something that’s on fire.”

Shortly afterward, the transit officials told riders that shuttle buses would replace service between Davis Square in Somerville and Park Street in Boston “due to a train with a mechanical problem” while personnel from the agency’s Car House responded to help getting the train moved. The third rail, which powers the trains, was being checked as well.

That was soon changed to the red line being shut down only between Harvard Square and Park Street, and riders were told to expect delays of at least an hour. By 10:36 a.m., that delay was extended by another hour.

By 11:35 a.m., shuttle buses were being phased out and train service resuming, though with delays, the MBTA said. Agency officials said there had never been a fire, just smoke from a mechanical issue.