The minor derailment is affecting service on Northeast Corridor and North Jersey Coast Line trains, as well as Amtrak.
It appears a car traveling behind the freight train left the tracks near the old General Motors property shortly before 6 a.m.
Workers were also looking for damage along the tracks.
Preliminary delays were reported at 15 to 30 minutes.
The train was moved and crews cleared by 6:30 a.m., but the delays were persisting.
