An overheated bearing likely sparked the fire that forced an MBTA ferry to divert to Castle Island and evacuate 25 passengers on Monday, the agency said.
The fire broke out about 2:30 p.m. as the ferry was heading from Hingham to Long Wharf in Boston. The vessel diverted to Castle Island, where passengers were able to safely disembark.
A preliminary investigation suggests a bearing became overheated and caused a small fire on the exterior surface of the bearing casing, an MBTA spokesperson said. The cause has not been finalized, and the MBTA and US Coast Guard continue to investigate, the spokesperson said.
The fire was quickly extinguished and no injuries were reported, transit officials said Monday. An MBTA bus took passengers from Castle Island to Long Wharf and the Aquarium MBTA station.
The ferry, named Champion, was later towed from Castle Island. The vessel was built in 2017 and underwent its most recent annual inspection in December, the MBTA said.
Ferry service continued Monday on other vessels.
The MBTA thanked responders from the Boston Fire Department and Massport Fire Rescue for their assistance.
Nick Stoico can be reached at nick.stoico@globe.com.