Shuttle buses replaced Green Line trains Thursday morning after a track maintenance vehicle derailed overnight, officials said.

"The MBTA apologizes for the disruption in service along the Green Line early this morning," an MBTA spokesperson said in a statement. "But regularly scheduled Green Line service has now resumed."

The track maintenance vehicle derailed around 4 a.m. between the Government Center and Park Street T stops, according to authorities.

Green Line service resumed at 6:45 a.m., transit officials said, after the vehicle was moved off the mainline.

No injuries were reported. The cause of the derailment remains under investigation.