A fire on the Orange Line tracks near Tufts Medical Center was caused by an overheated third rail insulator, an MBTA spokesperson said.

The incident, first reported by a train operator at 11:50 a.m. Wednesday, caused major delays on the Orange Line.

Service was suspended between North Station and Back Bay for more than an hour while the fire department investigated and the T’s power department made repairs, MBTA spokesperson Lisa Battiston said.

Regular service resumed, with delays, at approximately 2 p.m.

“The motorperson of a train at Tufts southbound reported flames within the track area in front of the train,” Battiston said. “It was subsequently determined that the incident was caused by an overheated third rail insulator.”

There were no injuries, she added.