A New Jersey Transit commuter train struck a tree on the tracks Monday, leaving the train operator dead and more than a dozen people injured.

The accident occurred shortly after 6 a.m. just north of the Roebling Station in Mansfield Township, NJ Transit said in a statement. There were 36 passengers aboard the River Line train, and television news video showed a large piece of the tree under the front of the train.

At least 16 people were treated for injuries not considered life-threatening, NJ Transit said. Authorities worked to determine how the tree ended up on the tracks.

River Line service was suspended in both directions between the Roebling and Trenton train stations, and sections of some nearby roads, including U.S. Highway 130, closed as authorities investigated.