mystery in Bridgewater

Authorities are investigating the burning of a track-repair car on an MBTA Commuter Rail track in Bridgewater, police said.

Bridgewater authorities said the fire occurred between Plymouth and Broad streets about 5:30 p.m.

From a nearby backyard barbecue, Justin Fuller, 22, said he saw the flames engulf the MBTA vehicle. He said it appeared a propane tank was attached to the machinery.

The MBTA did not immediately respond to calls.

“All of a sudden, we saw flames,” the Bridgewater State University student said in a telephone interview.

Then, he said, “There was a pretty big explosion just out of no where.”

Fuller said he did not think anyone was injured.

Firefighters arrived 10 minutes later and quickly extinguished the flames, Fuller said.